Monocrystal MFI molecular sieve nanosheet, preparation method thereof and method for preparing propylene from methanol

Abstract

The invention relates to the field of molecular sieve nanosheets, and discloses a monocrystal MFI molecular sieve nanosheet, a preparation method thereof and a method for preparing propylene from methanol. The molecular sieve nanosheet is an MFI type molecular sieve nanosheet; the micropore specific surface area of the molecular sieve nanosheet is 200-440m < 2 > / g; the total specific surface area of the molecular sieve nanosheet is 340-460 m < 2 > / g; the micropore volume of the molecular sieve nanosheet is 0.05 to 0.2 cm < 3 > / g; the mesoporous volume of the molecular sieve nanosheet is 0.02-0.2 cm < 3 > / g; the crystallinity of the molecular sieve nanosheet is 94-98%; the b-axis length of the molecular sieve nanosheet is not more than 210 nm. The molecular sieve nanosheet has the characteristics of small b-axis length, excellent shape selection performance and low synthesis cost.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve nanosheets, specifically to a single-crystal MFI molecular sieve nanosheet, its preparation method, and a method for producing propylene from methanol. Background Technology

[0002] MFI zeolite molecular sieves (including types such as S-1, TS-1, and ZSM-5) occupy a core position in various fields such as petrochemicals, fine catalysis, and gas separation due to their three-dimensional ten-membered ring cross-channel structure, tunable acidity, and excellent thermal stability. Typical applications include methanol-to-olefins (MTO), aromatic alkylation, and alkane dehydrogenation. However, traditional MFI zeolites suffer from a relatively large crystal size along the b-axis, resulting in longer straight channels that significantly increase molecular diffusion resistance, thus limiting the accessibility of active sites. This defect is particularly pronounced when processing large molecular or high-viscosity reactant systems, easily leading to catalyst deactivation due to carbon deposition. Taking the benzene-methanol alkylation reaction as an example, the longer straight channels of traditional ZSM-5 molecular sieves cause excessive methanol diffusion, not only initiating the formation of byproducts such as ethylbenzene but also increasing separation energy consumption. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of large b-axis length and high synthesis cost of traditional molecular sieve nanosheets in the prior art, and to provide a single-crystal MFI molecular sieve nanosheet, its preparation method and a method for producing propylene from methanol. The molecular sieve nanosheet has the characteristics of small b-axis length, excellent shape selectivity and low synthesis cost.

[0004] To achieve the above objectives, the first aspect of the present invention provides a molecular sieve nanosheet, wherein the molecular sieve nanosheet is an MFI type molecular sieve nanosheet; The specific surface area of ​​the micropores in the molecular sieve nanosheets is 200-440 m². 2 / g; The total specific surface area of ​​the molecular sieve nanosheets is 340-460 m². 2 / g; The molecular sieve nanosheets have a micropore volume of 0.05-0.2 cm³. 3 / g; The molecular sieve nanosheets have a mesopore volume of 0.02-0.2 cm³. 3 / g; The molecular sieve nanosheets have a crystallinity of 94-98%; The b-axis length of the molecular sieve nanosheets is no higher than 210 nm.

[0005] A second aspect of the present invention provides a method for preparing molecular sieve nanosheets, the method comprising: A first crystallization is performed on a first silicon source, a molecular sieve seed crystal, a first template agent, water, and optionally a heteroatom source to obtain molecular sieve nanosheets. The molecular sieve seed crystals are amorphous, and the total specific surface area of ​​the molecular sieve seed crystals is 400-900 m². 2 / g, microporous specific surface area is 20-500m² 2 / g, micropore volume is 0.01-0.2cm 3 / g, mesoporous pore volume is 0.05-0.7cm³ 3 / g; The first silicon source is calculated as silicon oxide, and the molar ratio of the first silicon source, the first template agent, and water is 1:0.02-0.5:15-150.

[0006] The third aspect of the present invention provides molecular sieve nanosheets prepared by the preparation method described in the second aspect above.

[0007] A fourth aspect of the present invention provides a method for producing propylene from methanol, the method comprising: In the presence of a carrier gas, methanol is reacted with molecular sieve nanosheets. The molecular sieve nanosheets are those described in the first and third aspects above.

[0008] Compared with the prior art, the present invention has the following beneficial effects through the above technical solution: (1) The b-axis length of the molecular sieve nanosheets in this invention is relatively short, which significantly shortens the molecular transport distance. At the same time, it can retain the excellent shape selectivity of the microporous molecular sieve nanosheets. Furthermore, the specific surface area of ​​the micropores, the total specific surface area, the micropore volume, the mesopore volume, and the crystallinity of the molecular sieve nanosheets are moderate, which can enhance the diffusion ability and improve the selectivity of propylene and the propylene / ethylene ratio of the molecular sieve nanosheets in methanol-to-propylene process. (2) By using specific amorphous seed crystals, compared with traditional crystalline seed crystals, amorphous seed crystals have high activity and high guiding ability. By controlling the amount of the first silicon source, the first template agent and water, nucleation can be induced more effectively and crystal growth kinetics can be regulated during the first crystallization process, thereby improving the performance of molecular sieve nanosheets. Attached Figure Description

[0009] Figure 1 (a) is a TEM (transmission electron microscope) image of PZ(Si). Figure 1 (b) is a TEM image of PZ(Ti)-40. Figure 1 (c) is a TEM image of PZ(Al)-200 and Figure 1 (d) is a TEM image of PZ(Al)-300; Figure 2These are the PXRD (powder X-ray diffraction) patterns of PZ(Si), PZ(Ti)-40, PZ(Al)-200, and PZ(Al)-300; Figure 3 (a) is a TEM image of IPZ(Si). Figure 3 (b) is a TEM image of IPZ(Al)-300; Figure 4 These are the PXRD patterns of IPZ(Si) and IPZ(Al)-300; Figure 5 The nitrogen adsorption-desorption curves are for PZ(Si), PZ(Ti)-40, PZ(Al)-200 and PZ(Al)-300. Figure 6 This is a nitrogen adsorption-desorption curve for IPZ(Si) and IPZ(Al)-300; Figure 7 The images show the PXRD patterns of samples prepared under different H2O / SiO2 molar ratios (x=15, 30, 60, 120). Figure 7 (a) is S-PZ-x, Figure 7 (b) is T-PZ-40-x, Figure 7 (c) Z-PZ-200-x, Figure 7 (d) is Z-PZ-300-x; Figure 8 (a) shows the PXRD patterns of S-PZ-120-5wt, T-PZ-40-120-5wt, Z-PZ-200-120-5wt, and Z-PZ-300-120-5wt. Figure 8 (b) are the PXRD patterns of S-IPZ-120, S-IPZ-120-5wt, Z-IPZ-300-120 and Z-IPZ-300-120-5wt; Figure 9Is S-PZ-15 (a1), S-PZ-30 (a2), S-PZ-60 (a3), S-PZ-120 (a4), S-PZ-120-5wt (a5), T-PZ-40-15 (b1) , T-PZ-40-30 (b2), T-PZ-40-60 (b3), T-PZ-40-120 (b4), T-PZ-40-120-5wt (b5), Z-PZ-200-15 (c1) , Z-PZ-200-30 (c2), Z-PZ-200-60 (c3), Z-PZ-200-120 (c4), Z-PZ-200-120-5wt (c5), Z-PZ-300-1 TEM images of 5 (d1), Z-PZ-300-30 (d2), Z-PZ-300-60 (d3), Z-PZ-300-120 (d4) and Z-PZ-300-120-5wt (d5); Figure 10 (a) is a TEM image of the S-IPZ-120. Figure 10 (b) is a TEM image of S-IPZ-120-5wt. Figure 10 (c) is a TEM image of Z-IPZ-300-120 and Figure 10 (d) is a TEM image of Z-IPZ-300-120-5wt; Figure 11 The graphs show the nitrogen adsorption-desorption curves of samples prepared under different H2O / SiO2 molar ratios (x = 15, 30, 60, 120). Figure 11 (a) is S-PZ-x, Figure 11 (b) is T-PZ-40-x, Figure 11 (c) is Z-PZ-200-x, and Figure 11 (d) is Z-PZ-300-x; Figure 12 (a) shows the nitrogen adsorption-desorption curves for S-PZ-120-5wt, T-PZ-40-120-5wt, Z-PZ-200-120-5wt, and Z-PZ-300-120-5wt. Figure 12 (b) is the nitrogen adsorption-desorption curve of S-IPZ-120, S-IPZ-120-5wt, Z-IPZ-300-120 and Z-IPZ-300-120-5wt; Figure 13 (a) is a TEM image of S-PZ-60-Scale. Figure 13 (b) is a Z-PZ-300-60-Scale TEM image; Figure 14(a) shows the PXRD patterns of S-PZ-60-Scale and Z-PZ-300-60-Scale. Figure 14 (b) is the nitrogen adsorption-desorption curve. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish between different materials or steps. For example, in "first calcination" and "second calcination," "first" and "second" simply indicate that they are not the same calcination process; similarly, in "first crystallization" and "second crystallization," "first" and "second" simply indicate that they are not the same crystallization process; in "first silicon source" and "second silicon source," "first" and "second" simply indicate that they are not the same silicon source; in "first template agent" and "second template agent," "first" and "second" simply indicate that they are not the same template agent; in "first aluminum source" and "second aluminum source," "first" and "second" simply indicate that they are not the same aluminum source.

[0012] The first aspect of this invention provides a molecular sieve nanosheet, wherein the molecular sieve nanosheet is an MFI type molecular sieve nanosheet; The specific surface area of ​​the micropores in the molecular sieve nanosheets is 200-440 m². 2 / g; The total specific surface area of ​​the molecular sieve nanosheets is 340-460 m². 2 / g; The molecular sieve nanosheets have a micropore volume of 0.05-0.2 cm³. 3 / g; The molecular sieve nanosheets have a mesopore volume of 0.02-0.2 cm³. 3 / g; The molecular sieve nanosheets have a crystallinity of 94-98%; The b-axis length of the molecular sieve nanosheets is no higher than 210 nm.

[0013] This invention controls the b-axis length and pore structure of molecular sieve nanosheets, which significantly shortens the diffusion path of substances in the micropores while maintaining the high crystallinity of the MFI framework, and synergistically improves the mass transfer efficiency between reactants and products, thereby enabling the molecular sieve nanosheets to exhibit high activity and selectivity in the methanol-to-propylene reaction.

[0014] According to the present invention, preferably, the crystallinity of the molecular sieve nanosheets is 95-97.6%, which is more conducive to the long service life of the molecular sieve nanosheets in the methanol-to-propylene reaction and to improving the selectivity of the target product.

[0015] In this invention, the crystallinity of the molecular sieve nanosheets was determined by Fourier transform infrared spectroscopy (FT-IR). Specifically, the crystallinity of the sample was measured at 550 cm⁻¹. -1 At 450 cm -1 The ratio of peak area to peak area I 550 / I 450 Dividing by 0.7 indicates the relative crystallinity of the sample. For example, the I of the sample... 550 / I 450 If the value is 0.67, then its relative crystallinity is 95.7%.

[0016] According to the present invention, preferably, the b-axis length of the molecular sieve nanosheet is 90-210 nm, which is beneficial to further shorten the molecular transport distance, while retaining the excellent shape selectivity of the molecular sieve nanosheet and making it less likely to cause the molecular sieve nanosheet to become deactivated due to carbon deposition. More preferably, it is 90-130 nm.

[0017] In this invention, the b-axis length of the molecular sieve nanosheets is obtained by testing TEM images and image analysis software. Specifically, the image analysis software uses its built-in measurement tools to statistically analyze all molecular sieve nanosheet samples in the TEM image, measure their b-axis lengths, and calculate the average value of the measured data to reduce errors. Finally, the statistically analyzed average data is compared with the known scale of the image, and the actual average b-axis length is obtained through scale conversion.

[0018] In this invention, the pore structure characteristics of molecular sieve nanosheets, such as micropore specific surface area, total specific surface area, micropore volume, and mesopore volume, are obtained by testing using a nitrogen physical adsorption-desorption method. Specifically, the micropore specific surface area and micropore volume are calculated using the t-plot method of nitrogen adsorption-desorption isotherms, the total specific surface area is calculated using the BET method, and the mesopore volume is calculated using the BJH method.

[0019] According to the present invention, preferably, the molecular sieve nanosheets are selected from at least one of all-silicon molecular sieve nanosheets, titanium-silicon molecular sieve nanosheets, and silicon-aluminum molecular sieve nanosheets.

[0020] According to the present invention, preferably, the molecular sieve nanosheets are all-silicon molecular sieve nanosheets.

[0021] According to the present invention, preferably, the surface area ratio (La+Lc) / Lb of the molecular sieve nanosheets is 10-54, more preferably 12-20.

[0022] In this invention, the aspect ratio (La+Lc) / Lb of the molecular sieve nanosheets is obtained by image analysis and statistical methods on TEM images. Specifically, image analysis software is used to measure the length of each crystal appearing in the TEM image (4000-8000 magnification) along the a, b, and c axes and take the average value, which is then recorded as La, Lb, and Lc, respectively. Subsequently, the average aspect ratio of each molecular sieve nanosheet sample is calculated according to the aspect ratio formula.

[0023] According to the present invention, preferably, the total specific surface area of ​​the molecular sieve nanosheets is 400-435 m². 2 / g.

[0024] According to the present invention, preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 210-430 m². 2 / g.

[0025] According to the present invention, preferably, the specific surface area of ​​the molecular sieve nanosheets is 3-210 m². 2 / g.

[0026] In this invention, the external specific surface area of ​​the molecular sieve nanosheets is calculated using the t-plot method of nitrogen adsorption-desorption isotherms.

[0027] According to the present invention, preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g.

[0028] According to the present invention, preferably, the mesopore volume of the molecular sieve nanosheets is 0.03-0.15 cm³. 3 / g.

[0029] In this invention, the all-silicon molecular sieve nanosheets meet the above-mentioned preferred range, which is more conducive to improving the mass transfer and diffusion efficiency of the molecular sieve nanosheets.

[0030] According to the present invention, preferably, the molecular sieve nanosheets are titanium-silicon molecular sieve nanosheets.

[0031] According to the present invention, preferably, the molar ratio of silicon oxide to titanium oxide in the molecular sieve nanosheets is 45-80:1, more preferably 50-72:1.

[0032] In this invention, the molar ratio of silicon oxide to titanium oxide in molecular sieve nanosheets is obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, after 10 mg of molecular sieve nanosheet sample is completely dissolved in acid, the concentrations of silicon and titanium elements in the solution are determined using an ICP instrument, and the molar ratio of silicon oxide to titanium oxide is calculated based on the measured values.

[0033] According to the present invention, preferably, the surface area ratio (La+Lc) / Lb of the molecular sieve nanosheets is 8-35, more preferably 8.4-34.8.

[0034] According to the present invention, preferably, the total specific surface area of ​​the molecular sieve nanosheets is 420-460 m². 2 / g.

[0035] According to the present invention, preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 210-450 m². 2 / g.

[0036] According to the present invention, preferably, the molecular sieve nanosheets have an external specific surface area of ​​10-220 m². 2 / g.

[0037] According to the present invention, preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g.

[0038] According to the present invention, preferably, the mesopore volume of the molecular sieve nanosheets is 0.02-0.15 cm³. 3 / g.

[0039] In this invention, the titanium-silicon molecular sieve nanosheets meet the above-mentioned preferred range, which is more conducive to improving the mass transfer and diffusion efficiency of the molecular sieve nanosheets.

[0040] According to the present invention, preferably, the molecular sieve nanosheets are silicon-aluminum molecular sieve nanosheets.

[0041] According to the present invention, preferably, in the aluminum NMR spectrum, the ZSM-5 molecular sieve nanosheets have no out-of-framework 5-coordinate and 6-coordinate aluminum sites.

[0042] In this invention, the ZSM-5 molecular sieve nanosheets have frameless 5-coordinate and 6-coordinate aluminum sites via... 27 Al magic angle rotation solid-state nuclear magnetic resonance (AL) 27 The molecular sieve nanosheets were obtained by Al MAS NMR (Al₂O₃) analysis. 27The Al MAS NMR spectrum showed that the resonance signal appeared only in the chemical shift range of 50-60 ppm, which was attributed to four-coordinate framework aluminum. Five-coordinate aluminum at approximately 30 ppm and six-coordinate aluminum at 0 ppm were not detected, indicating that the molecular sieve nanosheets do not contain extra-framework aluminum species.

[0043] According to the present invention, preferably, the total specific surface area of ​​the molecular sieve nanosheets is 340-440 m². 2 / g.

[0044] According to the present invention, preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 200-420 m². 2 / g.

[0045] According to the present invention, preferably, the specific surface area of ​​the molecular sieve nanosheets is 5-210 m². 2 / g.

[0046] According to the present invention, preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g.

[0047] According to the present invention, preferably, the mesopore volume of the molecular sieve nanosheets is 0.02-0.16 cm³. 3 / g.

[0048] According to the present invention, preferably, the Si / Al atomic ratio in the molecular sieve nanosheets is 100-180.

[0049] According to the present invention, preferably, the surface area ratio (La+Lc) / Lb of the molecular sieve nanosheets is 5-18, more preferably 5.5-16.

[0050] Preferably, the surface-to-height ratio (La+Lc) / Lb of ZSM-5 molecular sieve nanosheets with an atomic ratio of Si to Al of 105-125 is 5.6-12. Preferably, the surface-to-height ratio (La+Lc) / Lb of ZSM-5 molecular sieve nanosheets with an atomic ratio of Si to Al of 143-179 is 5.8-15.9.

[0051] In this invention, the silicon-aluminum molecular sieve nanosheets meet the above-mentioned preferred range, which is more beneficial to improving the service life of the molecular sieve nanosheets and the selectivity of the products in the methanol-to-propylene reaction.

[0052] A second aspect of the present invention provides a method for preparing molecular sieve nanosheets, the method comprising: A first crystallization is performed on a first silicon source, a molecular sieve seed crystal, a first template agent, water, and optionally a heteroatom source to obtain molecular sieve nanosheets. The molecular sieve seed crystals are amorphous, and the total specific surface area of ​​the molecular sieve seed crystals is 400-900 m². 2 / g, microporous specific surface area is 20-500m² 2 / g, micropore volume is 0.01-0.2cm 3 / g, mesoporous pore volume is 0.05-0.7cm³ 3 / g; The first silicon source is calculated as silicon oxide, and the molar ratio of the first silicon source, the first template agent, and water is 1:0.02-0.5:15-150.

[0053] This invention employs amorphous seed crystals with specific pore structure parameters. By precisely controlling the molar ratio of silicon source, template agent, and water, the b-axis length of MFI molecular sieve nanosheets can be precisely controlled. This method successfully prepares MFI molecular sieve nanosheets with high crystallinity, abundant hierarchical channels, and short b-axis characteristics. The process is highly controllable and has good repeatability.

[0054] In this invention, the optional heteroatom source means that a heteroatom source may or may not be added.

[0055] According to the present invention, preferably, before performing the first crystallization of the first silicon source, molecular sieve seed crystal, first template agent, water and optionally heteroatom source, the mixture of the first silicon source, molecular sieve seed crystal, first template agent, water and optionally heteroatom source is further included.

[0056] This invention does not impose any particular limitations on the mixing method and time, as long as the solution can be mixed evenly. Those skilled in the art can choose according to actual needs.

[0057] According to the present invention, preferably, the first crystallization is carried out in a fluorine-free system.

[0058] According to the present invention, preferably, the specific surface area of ​​the molecular sieve seed crystals is 20-800 m². 2 / g, preferably 700-800m 2 / g.

[0059] According to the present invention, preferably, the total specific surface area of ​​the molecular sieve seed crystals is 700-900 m². 2 / g, preferably 740-880 m 2 / g.

[0060] According to the present invention, preferably, the micropore specific surface area of ​​the molecular sieve seed crystals is 20-130 m². 2 / g, preferably 20-120 m 2 / g.

[0061] According to the present invention, preferably, the micropore volume of the molecular sieve seed crystals is 0.01-0.1 cm³. 3 / g, preferably 0.01-0.08cm 3 / g.

[0062] According to the present invention, preferably, the mesopore volume of the molecular sieve seed crystals is 0.3-0.9 cm³. 3 / g, preferably 0.4-0.8cm 3 / g.

[0063] In this invention, using molecular sieve seed crystals with physical properties that meet the above-mentioned preferred range can further improve the selectivity of the target product.

[0064] According to the present invention, preferably, the first silicon source is calculated as silicon oxide, and the molar ratio of the first silicon source, the first template agent and water is 1:0.03-0.05:15-120, which is more conducive to improving the selectivity of the target product in the methanol-to-propylene reaction of the prepared molecular sieve nanosheets, and reducing costs and environmental pollution.

[0065] According to the present invention, preferably, the mass content of molecular sieve seed crystals is 1-15%, more preferably 5-13%, based on the mass of silicon source (calculated as silicon oxide), which satisfies this preferred range and is more conducive to improving the selectivity of the target product.

[0066] The present invention has a wide range of choices for the type of first silicon source. Preferably, the first silicon source is silica sol and / or tetraethyl orthosilicate.

[0067] The present invention has a wide range of choices for the type of first template agent, as long as it can guide the synthesis of MFI molecular sieve nanosheets. Preferably, the first template agent is tetrapropylammonium hydroxide and / or tetrapropylammonium bromide, and more preferably tetrapropylammonium hydroxide.

[0068] According to the present invention, preferably, the molar ratio of the first silicon source to the heteroatom source, based on oxides, is 1:0.001-0.06, more preferably 1:0.0015-0.05.

[0069] According to the present invention, preferably, the heteroatom source is an aluminum source and / or a titanium source.

[0070] In this invention, preferably, the aluminum source and titanium source can be any soluble compound that can be calcined to obtain the corresponding alumina and titanium oxide, and this invention does not have any particular limitation.

[0071] More preferably, adding a Na-free aluminum source during the first crystallization process and adding a Na-containing aluminum source during the second crystallization process is more beneficial to improving the performance of molecular sieve nanosheets.

[0072] According to a preferred embodiment of the present invention, the heteroatom source is an aluminum source, and the method for preparing molecular sieve nanosheets further includes, after the first crystallization, subjecting the product after the first crystallization to a first calcination, ion exchange, and a second calcination.

[0073] According to the present invention, preferably, the present invention does not particularly limit the conditions of the first calcination, ion exchange and the second calcination, as long as the molecular sieve nanosheets with the specific characteristics mentioned above can be prepared, those skilled in the art can make the selection according to actual needs.

[0074] According to the present invention, preferably, the conditions for the first crystallization include a temperature of 120-170°C, more preferably 120-130°C.

[0075] According to the present invention, preferably, the conditions for the first crystallization include a time of 96-240 hours, more preferably 144-168 hours.

[0076] In this invention, the first crystallization conditions adopt the above-mentioned preferred range, which is more conducive to improving the selectivity of the target product in the methanol-to-propylene reaction of the obtained molecular sieve nanosheets.

[0077] According to the present invention, preferably, the method for preparing the molecular sieve seed crystals includes: The second silicon source, the second template agent, amino acids, water, and optionally a heteroatom source are subjected to a second crystallization and calcination.

[0078] According to the present invention, preferably, the second crystallization process further includes centrifugation, washing, and drying.

[0079] The present invention does not particularly limit the methods of centrifugation, washing, and drying, as long as the required seed crystals can be obtained. Those skilled in the art can choose according to actual needs.

[0080] According to the present invention, preferably, the molar ratio of the second silicon source, the second template agent, the amino acid and water, based on silicon oxide, is 1:0.4-0.5:0.3-0.4:7-15, more preferably 1:0.45-0.5:0.35-0.4:7-11.

[0081] The present invention has a wide range of choices for the type of second silicon source. Preferably, the second silicon source is silica sol and / or tetraethyl orthosilicate.

[0082] The present invention has a wide range of choices for the type of second template agent, as long as it can guide the synthesis of MFI molecular sieve nanosheets. Preferably, the second template agent is tetrapropylammonium hydroxide and / or tetrapropylammonium bromide, and more preferably tetrapropylammonium hydroxide.

[0083] In this invention, the amino acid includes at least one selected from glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, and histidine. Preferably, the amino acid is selected from at least one selected from lysine, proline, histidine, and arginine, with lysine being the most preferred.

[0084] In this invention, the use of amino acids within the above-mentioned preferred range, especially lysine, can yield seed crystals with higher activity. When preparing molecular sieve seed crystals, amino acids can improve the conversion rate of silicon source, which is more conducive to the long service life and high selectivity of the prepared molecular sieve nanosheets in the methanol-to-propylene reaction.

[0085] According to the present invention, preferably, the molar ratio of the second silicon source to the heteroatom source, based on oxides, is 1:0.001-0.035, more preferably 1:0.0015-0.03.

[0086] According to the present invention, preferably, the conditions for the second crystallization include a temperature of 90-120°C, more preferably 90-100°C.

[0087] According to the present invention, preferably, the conditions for the second crystallization include a time of 1-36 hours, more preferably 6-12 hours.

[0088] In this invention, the second crystallization conditions adopt the above-mentioned preferred range, which is more conducive to obtaining amorphous molecular sieve seed crystals containing the above-mentioned specific structure, thereby improving the selectivity of the target product in the methanol-to-propylene reaction of the molecular sieve nanosheets prepared by the amorphous molecular sieve seed crystals.

[0089] According to the present invention, preferably, the calcination conditions include a temperature of 500-600°C, more preferably 540-560°C.

[0090] According to the present invention, preferably, the calcination conditions include a time of 4-10 hours, more preferably 6-8 hours.

[0091] According to the present invention, preferably, the method for preparing the molecular sieve seed crystals further includes ball milling the second crystallized product and then performing the calcination.

[0092] According to the present invention, preferably, the ball milling conditions include: a frequency of 20-30 Hz, more preferably 25-30 Hz; and a time of 6-12 h, more preferably 9-10 h.

[0093] The third aspect of the present invention provides molecular sieve nanosheets prepared by the preparation method described in the second aspect above.

[0094] A fourth aspect of the present invention provides a method for producing propylene from methanol, the method comprising: In the presence of a carrier gas, methanol is reacted with molecular sieve nanosheets. The molecular sieve nanosheets are those described in the first and third aspects above.

[0095] In this invention, the above-mentioned contact reaction is beneficial to improving the selectivity of the target product.

[0096] According to the present invention, preferably, the carrier gas is nitrogen.

[0097] According to the present invention, preferably, the method further includes activating the molecular sieve nanosheets in a protective atmosphere before the contact reaction.

[0098] According to the present invention, preferably, the protective atmosphere is nitrogen.

[0099] According to the present invention, preferably, the activation conditions include a temperature of 400-420°C, more preferably 400-410°C.

[0100] According to the present invention, preferably, the activation conditions include a time of 1-3 hours, more preferably 1-2 hours.

[0101] According to the present invention, preferably, the conditions for the contact reaction include a temperature of 450-480°C, more preferably 470-480°C.

[0102] According to the present invention, preferably, the conditions for the methanol-to-propylene reaction include: a methanol space velocity of 1-12.5 h⁻¹. -1 Preferably 8-10.8h -1 .

[0103] According to a preferred embodiment of the present invention, molecular sieve nanosheets with a high aspect ratio can improve diffusion efficiency in the alkylation reaction of toluene and methanol, which is more conducive to improving the selectivity and yield of xylene.

[0104] The present invention will be described in detail below through embodiments.

[0105] Unless otherwise specified, all examples and comparative examples below are conventional methods; the reagents, materials and instruments used are commercially available and / or prepared using methods known in the art, unless otherwise specified.

[0106] In the following comparative examples and embodiments, lysine was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0107] The methods for characterizing the parameters involved in the following comparative examples and embodiments are as described above and will not be repeated here.

[0108] In the following comparative examples and embodiments, the testing methods for the a-axis and c-axis are the same as those for the b-axis described above, and will not be repeated here.

[0109] In the following comparative examples and embodiments, S-1 refers to all-silicon molecular sieve nanosheets, TS-1 refers to titanium-silicon molecular sieve nanosheets, and ZSM-5 refers to silicon-aluminum molecular sieve nanosheets.

[0110] The following preparation examples illustrate the preparation of seed crystals in this invention.

[0111] Preparation Example 1 A gel with a molar ratio of 1SiO2:0.46TPAOH:0.36L-lysine:9H2O was transferred to a hydrothermal reactor and crystallized at 90℃ for 12 h. After centrifugation, washing, and drying, pure silicon molecular sieve seed crystals were obtained and calcined at 550℃ for 6 h. The calcined sample was named PZ(Si).

[0112] TEM images such as Figure 1 As shown in (a), it can be seen from the figure that it exhibits amorphous characteristics and is composed of spherical particles with a particle size of about 20 nm.

[0113] PXRD such as Figure 2 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0114] Nitrogen adsorption-desorption curves are as follows Figure 5 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0115] Preparation Example 2 A gel with a molar ratio of 1 SiO2:0.025 TiO2:0.46 TPAOH:0.36 L-lysine:9H2O was transferred to a hydrothermal reactor and crystallized at 90℃ for 12 h. After centrifugation, washing, and drying, silicon-titanium molecular sieve seed crystals were obtained and calcined at 550℃ for 6 h. The calcined sample was named PZ(Ti)-40.

[0116] TEM image of the seed crystal as follows Figure 1 As shown in (b), it can be seen from the figure that it exhibits amorphous characteristics and is composed of spherical particles with a particle size of about 20 nm.

[0117] PXRD such as Figure 2 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0118] Nitrogen adsorption-desorption curves are as follows Figure 5 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0119] Preparation Example 3 A gel with a molar ratio of 1:0.025 SiO2:0.46 Al2O3:0.46 TPAOH:0.36 L-lysine:9H2O was transferred to a hydrothermal reactor and crystallized at 90℃ for 12 h. After centrifugation, washing, and drying, silica-alumina molecular sieve seed crystals were obtained and calcined at 550℃ for 6 h. The calcined sample was named PZ(Al)-200.

[0120] The conversion rate of the first silicon source is 99.3%. (Conversion rate of the first silicon source = mass of SiO2 in the seed crystal after calcination / mass of SiO2 fed in).

[0121] TEM image of the seed crystal as follows Figure 1 As shown in (c), it can be seen from the figure that it exhibits amorphous characteristics and is composed of spherical particles with a particle size of approximately 20 nm.

[0122] PXRD such as Figure 2 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0123] Nitrogen adsorption-desorption curves are as follows Figure 5 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0124] Preparation Example 4 A gel with a molar ratio of 1SiO2:0.017Al2O3:0.46TPAOH:0.36L-lysine:9H2O was transferred to a hydrothermal reactor and crystallized at 90℃ for 12 h. After centrifugation, washing, and drying, silica-alumina molecular sieve seed crystals were obtained and calcined at 550℃ for 6 h. The calcined sample was named PZ(Al)-300.

[0125] TEM image of the seed crystal as follows Figure 1 As shown in (d), it can be seen from the figure that it exhibits amorphous characteristics and is composed of spherical particles with a particle size of about 20 nm.

[0126] PXRD such as Figure 2 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0127] Nitrogen adsorption-desorption curves are as follows Figure 5 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0128] Preparation Example 5 2 g of uncalcined PZ(Si) solid powder and grinding balls were added to a ball mill jar. The sample was ball-milled at 30 Hz for 9 hours using a planetary ball mill (QM-3SP04, Nanjing University Equipment Factory), and then calcined at 550℃ for 6 hours to obtain PZ(Si) solid powder.

[0129] TEM Figure 3 As shown in (a), it can be seen from the figure that it has an amorphous structure and its morphology is a blocky particle with a size of about 500 nm.

[0130] PXRD such as Figure 4 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0131] Nitrogen adsorption-desorption curves are as follows Figure 6 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0132] Preparation Example 6 2 g of uncalcined PZ(Al)-300 solid powder and grinding balls were added to a ball mill jar. The sample was ball-milled at 30 Hz for 9 hours using a planetary ball mill (QM-3SP04, Nanjing University Equipment Factory), and then calcined at 550℃ for 6 hours. This yielded PZ(Al)-300 solid powder.

[0133] TEM Figure 3 As shown in (b), it can be seen from the figure that it has an amorphous structure and its morphology is a blocky particle with a size of about 500 nm.

[0134] PXRD such as Figure 4 As shown in the figure, no crystal diffraction peaks were observed, indicating that the sample has an amorphous structure.

[0135] Nitrogen adsorption-desorption curves are as follows Figure 6 As shown in the figure, it has a microporous-mesoporous structure, as detailed in Table 1.

[0136] Preparation Example 7 A gel with a molar ratio of 1SiO2:0.017Al2O3:0.5TPAOH:0.4L-lysine:11H2O was transferred to a hydrothermal reactor and crystallized at 100℃ for 8 h. After centrifugation, washing, and drying, silicon-aluminum molecular sieve seed crystals were obtained and named PZ(Al)-300-A. The crystals were then calcined at 560℃ for 6 h.

[0137] Preparation Example 8 The method of preparation example 3 was followed, except that lysine was replaced with valine in equimolar amounts.

[0138] The conversion rate of the first silicon source was 88.4%.

[0139] Preparation Example 9 The method was the same as in Preparation Example 3, except that the crystallization temperature was 120°C.

[0140] Preparation Example 10 The method of preparation example 3 is the same, except that 1SiO2:15H2O is used.

[0141] Comparative Preparation Example 1 The method of preparation example 3 is the same, except that 1SiO2:30H2O is used.

[0142] Table 1

[0143] The following examples illustrate the synthesis of molecular sieve nanosheets.

[0144] Example 1 Synthesis of S-1 zeolite nanosheets (S-PZ): In the synthesis of S-PZ, 0.13 g of PZ(Si) seed crystals (equivalent to 13% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.05 TPAOH:x H2O (x = 15, 30, 60, 120). After stirring overnight, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and crystallized at 120°C for 7 days. S-PZ samples prepared with H2O / SiO2 molar ratios of 15, 30, 60, and 120 were designated as S-PZ-15, S-PZ-30, S-PZ-60, and S-PZ-120, respectively.

[0145] The crystallinity of S-PZ-60 is 97.1%.

[0146] Figure 7 The PXRD patterns are those of samples prepared under different H2O / SiO2 molar ratios. The PXRD pattern of the sample prepared in this embodiment is shown below. Figure 7 As shown in (a), it can be seen from the figure that all samples exhibit typical MFI characteristic peaks and have good crystallinity.

[0147] The TEM of S-PZ-15 (a1), S-PZ-30 (a2), S-PZ-60 (a3), S-PZ-120 (a4) is as follows Figure 9 As shown in the figure, all samples exhibit a hexagonal nanosheet morphology with intact and clearly defined edges. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0148] Figure 11The nitrogen adsorption-desorption curves are shown for samples prepared under different H2O / SiO2 molar ratios. The nitrogen adsorption-desorption curve for this embodiment is shown below. Figure 11 As shown in (a), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0149] Example 2 PZ(Si) seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.05 TPAOH:xH2O (x=120). After stirring overnight, the mixture was transferred to a PTFE-lined stainless steel autoclave and crystallized at 120°C for 7 days. The S-PZ sample prepared with an H2O / SiO2 molar ratio of 120 was designated as S-PZ-120-5wt.

[0150] PXRD such as Figure 8 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0151] TEM Figure 9 As shown in Figure a5, the sample morphology is a hexagonal nanosheet with complete and clear edges. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0152] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (a), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0153] Example 3 In the synthesis of S-PZ, 0.13 g of IPZ(Si) seed crystals (equivalent to 13% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.05 TPAOH:x H2O (x=120). After stirring overnight, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and crystallized at 120°C for 7 days. The S-PZ sample prepared with an H2O / SiO2 molar ratio of 120 was designated as S-IPZ-120.

[0154] PXRD such as Figure 8 As shown in (b), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0155] TEM Figure 10 As shown in (a), the sample morphology is a hexagonal nanosheet with complete and clear edges; the specific average test data of axes a, b, and c and the results of the surface height ratio are shown in Table 3.

[0156] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (b), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0157] Example 4 In the synthesis of S-PZ, IPZ(Si) seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.05 TPAOH:x H2O (x=120). After stirring overnight, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and crystallized at 120°C for 7 days. The S-PZ sample prepared with an H2O / SiO2 molar ratio of 120 was designated as S-IPZ-120-5wt.

[0158] PXRD such as Figure 8 As shown in (b), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0159] TEM Figure 10 As shown in (b), the sample morphology is a hexagonal nanosheet with complete and clear edges. The specific average test data of axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0160] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (b), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0161] Example 5 Synthesis of TS-1 zeolite nanosheets (T-PZ-40): 0.13 g of PZ(Ti)-40 seed crystals (equivalent to 13% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2: 0.025 TiO2: 0.05 TPAOH: x H2O (x = 15, 30, 60, 120). After stirring overnight, the mixture was transferred to a reaction vessel and crystallized at 120℃ for 7 days. T-PZ-40 samples prepared with H2O / SiO2 molar ratios of 15, 30, 60, and 120 were designated as T-PZ-40-15, T-PZ-40-30, T-PZ-40-60, and T-PZ-40-120, respectively.

[0162] Figure 7 The PXRD patterns are those of samples prepared under different H2O / SiO2 molar ratios. The PXRD pattern of the sample prepared in this embodiment is shown below. Figure 7 As shown in (b), it can be seen from the figure that all samples exhibit typical MFI characteristic peaks and have good crystallinity.

[0163] TEM Figure 9 As shown in the figure, T-PZ-40-15 (b1), T-PZ-40-30 (b2), T-PZ-40-60 (b3), and T-PZ-40-120 (b4) all exhibit a hexagonal nanosheet morphology with intact and clearly defined edges. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0164] Figure 11 The nitrogen adsorption-desorption curves are shown for samples prepared under different H2O / SiO2 molar ratios. The nitrogen adsorption-desorption curve for this embodiment is shown below. Figure 11 As shown in (b), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0165] Example 6 Synthesis of TS-1 zeolite nanosheets (T-PZ-40): PZ(Ti)-40 seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1:SiO2:0.025:TiO2:0.05:TPAOH:x H2O (x = 120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120℃ for 7 days. The sample was designated as T-PZ-40-120-5wt.

[0166] PXRD such as Figure 8 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0167] TEM Figure 9 As shown in Figure b5, the sample morphology is a hexagonal nanosheet with complete and clear edges; the specific average test data of axes a, b, and c and the results of the surface height ratio are shown in Table 3.

[0168] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (a), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0169] Example 7 Synthesis of ZSM-5 zeolite nanosheets.

[0170] 0.13 g of PZ(Al)-200 seed crystals (equivalent to 13% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1SiO2:0.0025Al2O3:0.05TPAOH:xH2O (x = 15, 30, 60, 120). After stirring overnight, the mixture was transferred to a reaction vessel and crystallized at 120℃ for 7 days. Samples prepared under H2O / SiO2 molar ratios of 15, 30, 60, and 120 were designated as Z-PZ-200-15, Z-PZ-200-30, Z-PZ-200-60, and Z-PZ-200-120, respectively.

[0171] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0172] Figure 7 The images show the PXRD patterns of samples prepared under different H2O / SiO2 molar ratios. The PXRD pattern of the sample prepared in this embodiment is shown below. Figure 7 As shown in (c), it can be seen from the figure that all samples exhibit typical MFI characteristic peaks and have good crystallinity.

[0173] TEM Figure 9 As shown in the figure, Z-PZ-200-15 (c1), Z-PZ-200-30 (c2), Z-PZ-200-60 (c3), and Z-PZ-200-120 (c4) all exhibit a hexagonal nanosheet morphology with intact and clearly defined edges. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0174] Figure 11 The nitrogen adsorption-desorption curves are shown for samples prepared under different H2O / SiO2 molar ratios. The nitrogen adsorption-desorption curve for this embodiment is shown below. Figure 11 As shown in (c), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0175] The Si / Al atomic ratio and catalyst lifetime of Z-PZ-200-60 and Z-PZ-200-120 are shown in Table 4. The catalytic performance of the MTP reaction is shown in Table 5.

[0176] Example 8 Synthesis of ZSM-5 zeolite nanosheets.

[0177] PZ(Al)-200 seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.0025 Al2O3:0.05 TPAOH:x H2O (x=120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120℃ for 7 days. This result is denoted as Z-PZ-200-120-5wt.

[0178] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0179] PXRD such as Figure 8 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0180] TEM Figure 9 As shown in c5, the sample morphology is a hexagonal nanosheet with complete and clear edges; the specific average test data of the a, b, and c axes and the results of the surface height ratio are shown in Table 3.

[0181] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (a), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0182] Example 9 Synthesis of ZSM-5 zeolite nanosheets.

[0183] 0.13 g of PZ(Al)-300 seed crystals (equivalent to 13% of the mass of SiO2 in the silicon source) were added to a mixed gel with a molar ratio of 1SiO2:0.0017Al2O3:0.05TPAOH:xH2O (x = 15, 30, 60, 120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120°C for 7 days.

[0184] The samples prepared under H2O / SiO2 molar ratios of 15, 30, 60 and 120 are designated as Z-PZ-300-15, Z-PZ-300-30, Z-PZ-300-60 and Z-PZ-300-120, respectively.

[0185] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0186] Figure 7The PXRD patterns are those of samples prepared under different H2O / SiO2 molar ratios. The PXRD pattern of the sample prepared in this embodiment is shown below. Figure 7 As shown in (d), it can be seen from the figure that all samples exhibit typical MFI characteristic peaks and have good crystallinity.

[0187] TEM Figure 9 As shown in the figure, Z-PZ-300-15 (d1), Z-PZ-300-30 (d2), Z-PZ-300-60 (d3), and Z-PZ-300-120 (d4) all exhibit a hexagonal nanosheet morphology with intact and clearly defined edges. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0188] Figure 11 The nitrogen adsorption-desorption curves are shown for samples prepared under different H2O / SiO2 molar ratios. The nitrogen adsorption-desorption curve for this embodiment is shown below. Figure 11 As shown in (d), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0189] The Si / Al atomic ratio and catalyst lifetime of Z-PZ-300-60 and Z-PZ-300-120 are shown in Table 4. The catalytic performance of the MTP reaction is shown in Table 5.

[0190] Example 10 Synthesis of ZSM-5 zeolite nanosheets.

[0191] PZ(Al)-300 seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.0017Al2O3:0.05 TPAOH:x H2O (x=120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120℃ for 7 days. This result is denoted as Z-PZ-300-120-5wt.

[0192] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0193] PXRD such as Figure 8 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0194] TEM Figure 9 As shown in d5, the sample morphology is a hexagonal nanosheet with complete and clear edges; the specific average test data of the a, b, and c axes and the results of the surface height ratio are shown in Table 3.

[0195] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (a), it can be seen from the figure that it has a microporous-mesoporous structure. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0196] Example 11 Synthesis of ZSM-5 zeolite nanosheets.

[0197] 0.13 g of IPZ(Al)-300 seed crystals (equivalent to 13% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1SiO2:0.0017Al2O3:0.05TPAOH:xH2O (x=120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120℃ for 7 days. This was denoted as Z-IPZ-300-120.

[0198] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0199] PXRD such as Figure 8 As shown in (b), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0200] TEM Figure 10 As shown in (c), the sample morphology is a hexagonal nanosheet with complete and clear edges. The specific average test data of axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0201] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (b), the structure has a microporous-mesoporous configuration. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0202] Example 12 Synthesis of ZSM-5 zeolite nanosheets.

[0203] IPZ(Al)-300 seed crystals (equivalent to 5% of the SiO2 mass in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.0017Al2O3:0.05 TPAOH:x H2O (x=120). After stirring overnight, the mixture was transferred to a reactor and crystallized at 120℃ for 7 days. This result is denoted as Z-IPZ-300-120-5wt.

[0204] To obtain hydrogen-form ZSM-5 zeolite nanosheets, the sample was calcined at 550 °C to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80 °C for 6 hours, and finally calcined at 550 °C for 6 hours.

[0205] PXRD such as Figure 8 As shown in (b), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0206] TEM Figure 10 As shown in (d), the sample morphology is a hexagonal nanosheet with complete and clear edges. The specific average test data of axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0207] Nitrogen adsorption-desorption curves are shown below Figure 12 As shown in (b), the structure has a microporous-mesoporous configuration. The specific surface area of ​​the micropores, the total specific surface area, and the volume of the mesopores are shown in Table 2.

[0208] Example 13 The seed crystals obtained in Preparation Example 7 (equivalent to 10% of the mass of SiO2 in the silicon source) were added to a mixed gel with a molar ratio of 1 SiO2:0.017 Al2O3:0.03 TPAOH:60H2O. After stirring overnight, the mixture was transferred to a reaction vessel and crystallized at 130°C for 144 h. This was designated as Z-PZ-300-60-A.

[0209] The sample was calcined at 550℃ to remove the organic template, followed by ion exchange in 1M NH4Cl solution at 80℃ for 6 hours, and finally calcined again at 550℃ for 6 hours. The performance parameters are shown in Tables 2 and 3.

[0210] Example 14 The method of Example 8 was followed, except that the seed crystals of the same quality were replaced with those obtained in Preparation Example 8. The performance parameters are shown in Tables 2 and 3.

[0211] Example 15 The method of Example 8 was followed, except that the seed crystals of the same quality were replaced with those obtained in Preparation Example 9. The performance parameters are shown in Tables 2 and 3.

[0212] Example 16 The method of Example 8 was followed, except that the seed crystals of the same quality were replaced with those obtained in Preparation Example 10. The performance parameters are shown in Tables 2 and 3.

[0213] Example 17 The method of Example 8 was followed, except that the crystallization temperature of 120°C in Example 8 was replaced with 170°C. The performance parameters are shown in Tables 2 and 3.

[0214] Comparative Example 1 The method of Example 8 was followed, except that the seed crystals of equal quality were replaced with those obtained in Comparative Preparation Example 1. The results are shown in Tables 2, 3, and 5.

[0215] Comparative Example 2 The method was followed in Example 8, except that the 1 SiO2:120 H2O water was replaced with 1 SiO2:200 H2O. The results are shown in Tables 2, 3 and 5.

[0216] Test Example 1 S-1 zeolite (S-PZ-60-Scale) and ZSM-5 zeolite (Z-PZ-300-60-Scale) were synthesized in a 5L scale-up reactor using the same method as the synthesis methods for S-PZ-60 and Z-PZ-300-60 described above.

[0217] S-PZ-60-Scale TEM Figure 13 As shown in (a), the scaled-up synthesized S-1 samples all maintain a hexagonal nanosheet morphology and exhibit good crystallinity. The specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0218] S-PZ-60-Scale PXRD such as Figure 14 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0219] The nitrogen adsorption-desorption characterization results of S-PZ-60-Scale are as follows: Figure 14 As shown in (b), it can be seen from the figure that it has typical microporous characteristics.

[0220] Z-PZ-300-60-Scale TEM, such as Figure 13 As shown in (b), the scaled-up synthesized S-1 samples all maintain a hexagonal nanosheet morphology and exhibit good crystallinity. Specific average test data for axes a, b, and c, as well as the surface-to-height ratio results, are shown in Table 3.

[0221] The PXRD of Z-PZ-300-60-Scale is as follows: Figure 14 As shown in (a), it can be seen from the figure that it exhibits typical MFI characteristic peaks and has good crystallinity.

[0222] The nitrogen adsorption-desorption characterization results of Z-PZ-300-60-Scale are as follows: Figure 14 As shown in (b), it can be seen from the figure that it has typical microporous characteristics.

[0223] Table 2

[0224] Table 3

[0225] Note: Traditional ZSM-5 is prepared using the method described in the literature Ahmadpour, J.; Taghizadeh, M. Catalytic conversion of methanol to propylene over high-silica mesoporous ZSM-5 zeolites prepared by different combinations of mesogenous templates. J. Nat. Gas. Sci. Eng. 2015, 23, 184-194. The commercial ZSM-5 was purchased from Tianjin Nanhua Catalyst Co., Ltd., and its grade was NKF-5. In this invention, "-" indicates that there is no test result.

[0226] The data above show that the molecular sieve nanosheets prepared in this invention have a short b-axis length and good crystallinity. The short b-axis of the silica-alumina molecular sieve nanosheets is beneficial for improving the selectivity of propylene and the propylene / ethylene ratio in the MTP reaction. The all-silicon molecular sieve nanosheets, due to their short b-axis and excellent shape selectivity, effectively improve their efficiency and rate in the separation of xylene isomers. The short b-axis of the titanium-silicon molecular sieve nanosheets effectively improves the selectivity of 1,2-epoxyhexane in the 1-hexene epoxidation reaction.

[0227] Test Example 2 MTP Catalytic Testing: The catalytic performance of the MTP reaction was tested in a quartz tube fixed-bed reactor under normal pressure (1 atm) using molecular sieve nanosheets (see Tables 4 and 5) prepared in the above examples and comparative examples, conventional ZSM-5 (93.5% crystallinity), and commercial ZSM-5 (96.6% crystallinity). Molecular sieve nanosheets (50 mg, 40-60 mesh) were packed into quartz tubes with an inner diameter of 6 mm. Before each reaction, the atmosphere was saturated with nitrogen (flow rate 100 mL / min). -1 The mixture was activated in situ at 400℃ for 1 h, and then the temperature was increased to the reaction temperature of 470℃. Methanol was fed through a saturator as a carrier gas, with the space velocity (WHSV) controlled at 8 h⁻¹. -1The reaction products were analyzed online using a gas chromatograph (Agilent GC 7890A) equipped with one thermal conductivity detector (TCD), two flame ionization detectors (FID), and two capillary columns (J&W 127-7031, 30 m × 530 μm × 0.25 μm; Agilent 19095P-S25, 50 m × 530 μm × 15 μm). Methanol conversion (x) and hydrocarbon selectivity (yi) were calculated using the following formulas:

[0228]

[0229] In the formula, n _(methanol,in) n represents the molar amount of methanol in the reaction feed. _(methanol,out) This represents the molar amount of methanol detected at the reaction outlet. n i k is the molar amount of target product i among all the products reacted. i The number of carbon atoms in its molecule. Methanol and dimethyl ether are considered unreacted reactants.

[0230] The test results are shown in Tables 4 and 5.

[0231] Table 4

[0232] Note: Catalyst lifetime refers to the time from the initial reaction to when the methanol conversion rate decreases to 90%.

[0233] Table 5

[0234] Note: q refers to the molar ratio of propylene to ethylene; light olefins refer to the sum of the selectivity of ethylene, propylene, and butene.

[0235] The results show that, compared with the comparative example, the molecular sieve nanosheets provided by this invention or the molecular sieve nanosheet catalyst prepared by its preparation method not only have a longer catalytic lifetime, better propylene selectivity and a higher propylene / ethylene ratio, but also have a shorter b-axis length and excellent shape selectivity, and the synthesis cost is lower. The molecular sieve nanosheets with a short b-axis length prepared by this invention are beneficial to improving the ethylene selectivity in the MTP reaction, effectively overcoming the defects of traditional molecular sieve nanosheets in the prior art, such as large b-axis length, high synthesis cost and low ethylene selectivity in the MTP reaction.

[0236] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A molecular sieve nanosheet, characterized in that, The molecular sieve nanosheets are MFI type molecular sieve nanosheets; The specific surface area of ​​the micropores in the molecular sieve nanosheets is 200-440 m². 2 / g; The total specific surface area of ​​the molecular sieve nanosheets is 340-460 m². 2 / g; The molecular sieve nanosheets have a micropore volume of 0.05-0.2 cm³. 3 / g; The molecular sieve nanosheets have a mesopore volume of 0.02-0.2 cm³. 3 / g; The molecular sieve nanosheets have a crystallinity of 94-98%; The b-axis length of the molecular sieve nanosheets is no higher than 210 nm.

2. The molecular sieve nanosheets according to claim 1, wherein, The crystallinity of the molecular sieve nanosheets is 95-97.6%; Preferably, the b-axis length of the molecular sieve nanosheet is 90-210 nm, more preferably 90-130 nm; Preferably, the molecular sieve nanosheets are selected from at least one of all-silicon molecular sieve nanosheets, titanium-silicon molecular sieve nanosheets, and silicon-aluminum molecular sieve nanosheets.

3. The molecular sieve nanosheets according to claim 2, wherein, The molecular sieve nanosheets are all-silicon molecular sieve nanosheets; Preferably, the aspect ratio (La+Lc) / Lb of the molecular sieve nanosheets is 10-54, more preferably 12-20; Preferably, the total specific surface area of ​​the molecular sieve nanosheets is 400-435 m². 2 / g; Preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 210-430 m². 2 / g; Preferably, the molecular sieve nanosheets have an external specific surface area of ​​3-210 m². 2 / g; Preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g; Preferably, the mesopore volume of the molecular sieve nanosheets is 0.03-0.15 cm³. 3 / g.

4. The molecular sieve nanosheets according to claim 2, wherein, The molecular sieve nanosheets are titanium-silicon molecular sieve nanosheets; Preferably, the molar ratio of silicon dioxide to titanium dioxide in the molecular sieve nanosheets is 45-80:1, more preferably 50-72:1; Preferably, the aspect ratio (La+Lc) / Lb of the molecular sieve nanosheets is 8-35, more preferably 8.4-34.8; Preferably, the total specific surface area of ​​the molecular sieve nanosheets is 420-460 m². 2 / g; Preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 210-450 m². 2 / g; Preferably, the molecular sieve nanosheets have an external specific surface area of ​​10-220 m². 2 / g; Preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g; Preferably, the mesopore volume of the molecular sieve nanosheets is 0.02-0.15 cm³. 3 / g.

5. The molecular sieve nanosheets according to claim 2, wherein, The molecular sieve nanosheets are silica-alumina molecular sieve nanosheets; Preferably, in the aluminum NMR spectrum, the ZSM-5 molecular sieve nanosheets have no out-of-framework 5-coordinate and 6-coordinate aluminum sites; Preferably, the total specific surface area of ​​the molecular sieve nanosheets is 340-440 m². 2 / g; Preferably, the microporous specific surface area of ​​the molecular sieve nanosheets is 200-420 m². 2 / g; Preferably, the molecular sieve nanosheets have an external specific surface area of ​​5-210 m². 2 / g; Preferably, the micropore volume of the molecular sieve nanosheets is 0.08-0.2 cm³. 3 / g; Preferably, the mesopore volume of the molecular sieve nanosheets is 0.02-0.16 cm³. 3 / g; Preferably, the Si / Al atomic ratio in the molecular sieve nanosheets is 100-180; Preferably, the surface area ratio (La+Lc) / Lb of the molecular sieve nanosheets is 5-18, more preferably 5.5-16.

6. A method for preparing molecular sieve nanosheets, characterized in that, The method includes: A first crystallization is performed on a first silicon source, a molecular sieve seed crystal, a first template agent, water, and optionally a heteroatom source to obtain molecular sieve nanosheets. The molecular sieve seed crystals are amorphous, and the total specific surface area of ​​the molecular sieve seed crystals is 400-900 m². 2 / g, microporous specific surface area is 20-500m² 2 / g, micropore volume is 0.01-0.2cm 3 / g, mesoporous pore volume is 0.05-0.7cm³ 3 / g; The first silicon source is calculated as silicon oxide, and the molar ratio of the first silicon source, the first template agent, and water is 1:0.02-0.5:15-150.

7. The preparation method according to claim 6, wherein, The specific surface area of ​​the molecular sieve seed crystals is 20-800 m². 2 / g, preferably 700-800m 2 / g; Preferably, the total specific surface area of ​​the molecular sieve seed crystals is 700-900 m². 2 / g, preferably 740-880 m 2 / g; Preferably, the microporous specific surface area of ​​the molecular sieve seed crystals is 20-130 m². 2 / g, preferably 20-120 m 2 / g; Preferably, the micropore volume of the molecular sieve seed crystals is 0.01-0.1 cm³. 3 / g, preferably 0.01-0.08cm 3 / g; Preferably, the mesopore volume of the molecular sieve seed crystals is 0.3-0.9 cm³. 3 / g, preferably 0.4-0.8cm 3 / g.

8. The preparation method according to claim 6 or 7, wherein, The molar ratio of the first silicon source (based on silicon oxide), the first template agent, and water is 1:0.03-0.05:15-120. Preferably, based on the mass of the silicon source (calculated as silicon oxide), the mass content of the molecular sieve seed crystals is 1-15%, more preferably 5-13%; Preferably, the first silicon source is silica sol and / or tetraethyl orthosilicate; Preferably, the first template agent is tetrapropylammonium hydroxide and / or tetrapropylammonium bromide, more preferably tetrapropylammonium hydroxide; Preferably, the molar ratio of the first silicon source to the heteroatom source, based on oxides, is 1:0.001-0.06, more preferably 1:0.0015-0.05; Preferably, the heteroatom source is an aluminum source and / or a titanium source; Preferably, the conditions for the first crystallization include: a temperature of 120-170°C, more preferably 120-130°C; and a time of 96-240 h, more preferably 144-168 h.

9. The preparation method according to any one of claims 6-8, wherein, The method for preparing the molecular sieve seed crystals includes: The second silicon source, the second template agent, amino acids, water, and optionally a heteroatom source are subjected to a second crystallization and calcination. Preferably, the molar ratio of the second silicon source (based on silicon oxide), the second template agent, the amino acid, and water is 1:0.4-0.5:0.3-0.4:7-15, and more preferably 1:0.45-0.5:0.35-0.4:7-11. Preferably, the second silicon source is silica sol and / or tetraethyl orthosilicate; Preferably, the second template agent is tetrapropylammonium hydroxide and / or tetrapropylammonium bromide, more preferably tetrapropylammonium hydroxide; Preferably, the amino acid is lysine; Preferably, the molar ratio of the second silicon source to the heteroatom source, based on oxides, is 1:0.001-0.035, more preferably 1:0.0015-0.03; Preferably, the conditions for the second crystallization include: a temperature of 90-120°C, more preferably 90-100°C; and a time of 1-36 hours, more preferably 6-12 hours. Preferably, the calcination conditions include: a temperature of 500-600℃, more preferably 540-560℃; and a time of 4-10h, more preferably 6-8h.

10. The preparation method according to claim 9, wherein, The method for preparing the molecular sieve seed crystals further includes ball milling the second crystallized product and then calcining it. Preferably, the ball milling conditions include: a frequency of 20-30Hz, more preferably 25-30Hz; and a time of 6-12h, more preferably 9-10h.

11. Molecular sieve nanosheets prepared by the preparation method according to any one of claims 6-10.

12. A method for producing propylene from methanol, characterized in that, The method includes: In the presence of a carrier gas, methanol is reacted with molecular sieve nanosheets. The molecular sieve nanosheets are the molecular sieve nanosheets described in any one of claims 1-5 and claim 11; Preferably, the method further includes activating the molecular sieve nanosheets in a protective atmosphere before the contact reaction; Preferably, the activation conditions include: a temperature of 400-420℃; and a time of 1-3 hours. Preferably, the conditions for the contact reaction include: a temperature of 450-480°C; and a methanol space velocity of 1-12.5 h⁻¹. -1 .

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