Preparation method for ZSM-5 molecular sieve

Abstract

The present application provides a preparation method for a ZSM-5 molecular sieve, comprising the following steps: 1) heating and stirring a first system comprising a silicon source and an alkaline solution until the first system becomes clear, then adding an aluminum source and water to the first system to obtain a second system, and adding a silicate-1 seed to the second system to obtain a first gel, the wherein the silicate-1 seed has a tetrapropylammonium content of 0-40%; and 2) subjecting the first gel to a first aging treatment and a first crystallization treatment to obtain a ZSM-5 molecular sieve, wherein the ZSM-5 molecular sieve is any one of the following: spherical, regular hexagonal, or nanosheet layered. The preparation method for the ZSM-5 molecular sieve provided in the present application exhibits good process stability and high yield, and does not require additional structure-directing agents. The preparation method is low cost, easy to operate, generates wastewater that is easy to treat, and is therefor conducive to large-scale industrial production.

Description

A method for preparing ZSM-5 molecular sieve

[0001] This application claims priority to Chinese Patent Application No. 202411532990.3, filed on October 30, 2024, entitled “A Method for Preparing ZSM-5 Molecular Sieves”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of molecular sieve technology, and in particular relates to a method for preparing ZSM-5 molecular sieve. Background Technology

[0003] ZSM-5 molecular sieves, due to their regular and abundant pore structure, diverse framework element composition, controllable acidity, and good hydrothermal stability, not only play an important role in traditional fields such as adsorption, separation, and catalysis, but also occupy an important position in emerging fields such as CO2 conversion, oil-water separation, energy storage, nuclear waste treatment, and biomass conversion. Furthermore, the morphology and size of ZSM-5 molecular sieves required vary depending on the application. For example, for layered nanosheet ZSM-5 molecular sieves, the thinner nanosheets have shorter mass transfer paths, which is beneficial for molecular diffusion and results in superior mass transfer performance compared to other morphologies of molecular sieves, exhibiting a significant advantage in catalytic conversion reactions involving macromolecules.

[0004] CN116078421A discloses a method for preparing a highly stable nanoscale ZSM-5 catalyst and its application. The method employs a seed crystal method, using all-silica molecular sieve silicalite-1 as a seed crystal. The catalyst is mixed with reactants and pre-crystallized, followed by crystallization, ammonia exchange, and metal loading to obtain the ZSM-5 catalyst. This preparation method is environmentally friendly, requires minimal equipment, and produces a catalyst with high feed conversion rate and high aromatic selectivity in light alkane aromatization systems, while also exhibiting good stability. However, the synthesized nanoscale ZSM-5 molecular sieve consists of secondary small particles of approximately 50 nm, failing to address the issue of the relatively large particle size of the ZSM-5 molecular sieve.

[0005] CN115490243A discloses a short b-axis HZSM-5 zeolite molecular sieve, its preparation method, and its application. The method involves preparing a silicalite-1 seed suspension; preparing a precursor solution; preparing a dry gel; hydrothermal crystallization; and preparing H-type ZSM-5 to obtain the short b-axis HZSM-5 zeolite molecular sieve. This molecular sieve is applied to the synthesis of aromatics from syngas, using carbon monoxide and hydrogen as reactants, achieving an aromatic selectivity of over 80% and a light aromatic content of over 70%. However, the HZSM-5 zeolite molecular sieve prepared by this method still suffers from a relatively large particle size.

[0006] Therefore, in the existing technology, the ZSM-5 molecular sieves produced by the preparation method have large particle sizes and use a large amount of organic template agents, which have disadvantages such as high cost, complicated operation process and difficult wastewater treatment, making it difficult to realize industrial production. Summary of the Invention

[0007] The main objective of this application is to provide a method for preparing ZSM-5 molecular sieves. The ZSM-5 molecular sieves prepared by this method have small particle sizes, do not require the addition of template agents, are low in cost, simple to operate, and produce easily treatable wastewater, which is conducive to large-scale industrial production.

[0008] This application provides a method for preparing ZSM-5 molecular sieve, comprising the following steps:

[0009] 1) The first system, including silicon source and alkaline solution, is heated and stirred until it becomes clear. Then, aluminum source and water are added to the first system to obtain the second system. Silicate-1 seed crystals are added to the second system to obtain the first gel.

[0010] The tetrapropylammonium content in the Silicate-1 seed crystal is 0-40%;

[0011] 2) The first gel is subjected to a first aging treatment and a first crystallization treatment to obtain the ZSM-5 molecular sieve;

[0012] The ZSM-5 molecular sieve is any one of spherical, regular hexagonal, or nanosheet layered molecular sieves.

[0013] In the preparation method described above, the ZSM-5 molecular sieve is a spherical molecular sieve with a particle size of 90-150 nm; the tetrapropylammonium content X in the Silicate-1 seed crystal is 11% < X ≤ 40%.

[0014] In the preparation method described above, the average particle size of the Silicate-1 seed crystal is 20-30 nm.

[0015] As described above, the ZSM-5 molecular sieve is a regular hexagonal molecular sieve with an a-axis length of 60-100 nm, a b-axis length of 50-70 nm, and a c-axis length of 100-150 nm; the tetrapropylammonium content Y in the Silicate-1 seed crystal is 0 < Y ≤ 11%.

[0016] As described above, the ZSM-5 molecular sieve is a nanosheet-like layered molecular sieve with an a-axis length of 80-160 nm, a b-axis length of 10-50 nm, and a c-axis length of 200-700 nm; the tetrapropylammonium content Z in the Silicate-1 seed crystal is 0%.

[0017] As described above, the Silicate-1 seed crystal is obtained from Silicate-1 seed mother liquor. The Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation, washing, redispersing, drying, and calcination to obtain Silicate-1 seed crystal with a tetrapropylammonium content of 0-40%.

[0018] In the preparation method described above, the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel is 1:0.00025-0.05:0.08-1:10-120:0.001-0.5; and / or,

[0019] The first aging treatment is performed at a temperature of 30-100℃ for a time of 6-12 hours; and / or,

[0020] The temperature of the first crystallization treatment is 120-180℃, and the time is 12-48h.

[0021] The Silicate-1 seed solution is prepared by the method described above, comprising the following steps:

[0022] 1) The system, including silicon source, alkaline solution, organic template agent and water, is subjected to hydrolysis to obtain a second gel;

[0023] 2) The second gel is subjected to a second aging treatment and a second crystallization treatment to obtain the Silicate-1 seed mother liquor.

[0024] In the preparation method described above, the molar ratio of silicon dioxide in the silicon source, hydroxide ions in the alkaline solution, organic template agent, and water is 1:0.01-1:0.01-1:4-100; and / or,

[0025] The second aging treatment is performed at a temperature of 30-80℃ for 1-7 days; and / or,

[0026] The second crystallization treatment is carried out at a temperature of 100-170℃ for 12-24 hours.

[0027] The preparation method described above further includes: cooling the product of the second aging treatment at 0-20°C.

[0028] The method for preparing ZSM-5 molecular sieves provided in this application can achieve the preparation of ZSM-5 molecular sieves with different morphologies by adjusting the content of tetrapropylammonium in Silicate-1 seed crystals. The ZSM-5 molecular sieves prepared by this method have small particle size, do not require the addition of template agents, are low in cost, simple to operate, and the wastewater generated is easy to treat, which is conducive to realizing large-scale industrial production. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments of this application or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 is a SEM image of the Silicate-1 seed crystals prepared in Example 1 of this application;

[0031] Figure 2 is a SEM image of the Silicate-1 seed crystals prepared in Comparative Example 2 of this application;

[0032] Figure 3 is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 2 of this application;

[0033] Figure 4 is a SEM image of the spherical ZSM-5 molecular sieve prepared in Example 1 of this application;

[0034] Figure 5 is a SEM image of the regular hexagonal ZSM-5 molecular sieve prepared in Example 2 of this application;

[0035] Figure 6 is a SEM image of the nanosheet-layered ZSM-5 molecular sieve prepared in Example 3 of this application;

[0036] Figure 7 is a TEM image of the nanosheet-like ZSM-5 molecular sieve prepared in Example 3 of this application;

[0037] Figure 8 is a SEM image of the nanosheet-layered ZSM-5 molecular sieve prepared in Example 4 of this application;

[0038] Figure 9 is a SEM image of the nanosheet-layered ZSM-5 molecular sieve prepared in Example 5 of this application;

[0039] Figure 10 is a TEM image of the nanosheet-like ZSM-5 molecular sieve prepared in Example 5 of this application;

[0040] Figure 11 shows the XRD patterns of the ZSM-5 molecular sieves prepared in Examples 1-3 and Comparative Examples 1-2 of this application;

[0041] Figure 12 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 1 of this application under a scanning electron microscope;

[0042] Figure 13 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 2 of this application under a scanning electron microscope;

[0043] Figure 14 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 3 of this application under a scanning electron microscope;

[0044] Figure 15 shows the physical adsorption curves of the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 of this application;

[0045] Figure 16 shows the pore size distribution of the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 of this application. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] This application provides a method for preparing ZSM-5 molecular sieve, comprising the following steps:

[0048] 1) The first system, including silicon source and alkaline solution, is heated and stirred until it becomes clear. Then, aluminum source and water are added to the first system to obtain the second system. Silicate-1 seed crystals are added to the second system to obtain the first gel.

[0049] The tetrapropylammonium content in the Silicate-1 seed crystal is 0-40%;

[0050] 2) The first gel is subjected to a first aging treatment and a first crystallization treatment to obtain the ZSM-5 molecular sieve;

[0051] The ZSM-5 molecular sieve is any one of spherical, regular hexagonal, or nanosheet layered molecular sieves.

[0052] This application aims to prepare spherical, regular hexagonal, and nanosheet-layered ZSM-5 molecular sieves, which can be achieved by controlling the content of tetrapropylammonium in Silicate-1 seed crystals.

[0053] Specifically, in step 1), a silicon source and an alkaline solution are mixed in a certain proportion to obtain a first system. The first system is heated and stirred until clear. An aluminum source and water are then added to the first system, and the mixture is stirred at 20-25°C for a certain time to obtain a second system. Silicate-1 seed crystals are added to the second system to obtain a first gel, wherein the tetrapropylammonium content in the Silicate-1 seed crystals is 0-40%. The silicon source can be at least one of tetraethyl orthosilicate, silica sol, silicic acid, water glass, and fumed silica, preferably tetraethyl orthosilicate. The aluminum source can be at least one of aluminum hydroxide, sodium aluminate, aluminum sulfate octadecylhydrate, aluminum chloride hexahydrate, and aluminum chloride, preferably aluminum sulfate octadecylhydrate. The alkaline solution can be a sodium hydroxide solution.

[0054] In step 2), the first gel is subjected to a first aging treatment and a first crystallization treatment to obtain ZSM-5 molecular sieve. This application does not limit the temperature and time of the first aging treatment and the first crystallization treatment, as long as ZSM-5 molecular sieve can be obtained. Because the tetrapropylammonium content in the Silicate-1 seed crystal added in step 1) is 0-40%, the prepared ZSM-5 molecular sieve can be any of the following: spherical, hexagonal, or nanosheet-layered ZSM-5 molecular sieve.

[0055] The method for preparing ZSM-5 molecular sieves provided in this application can achieve the preparation of ZSM-5 molecular sieves with different morphologies by adjusting the content of tetrapropylammonium in Silicate-1 seed crystals. The ZSM-5 molecular sieves prepared by this method have small particle size, do not require the addition of template agents, are low in cost, simple to operate, and the wastewater generated is easy to treat, which is conducive to realizing large-scale industrial production.

[0056] In some embodiments of this application, the ZSM-5 molecular sieve is a spherical molecular sieve with a particle size of 90-150 nm; the tetrapropylammonium content X in the Silicate-1 seed crystal is 11% < X ≤ 40%.

[0057] In this application, when the tetrapropylammonium content X in the Silicate-1 seed crystal is controlled to be 11% < X ≤ 40%, the prepared ZSM-5 molecular sieve is a spherical molecular sieve with a particle size of 90-150 nm, which can precisely control the size and morphology of the molecular sieve.

[0058] In some embodiments of this application, the average particle size of the Silicate-1 seed crystal is 20-30 nm.

[0059] In this application, the average particle size of Silicate-1 seed crystals is controlled to be 20-30 nm, which is beneficial to control the particle size of the subsequently prepared regular hexagonal molecular sieves and nanosheet layered molecular sieves, giving them diffusion advantages in the b-axis direction.

[0060] In some embodiments of this application, the ZSM-5 molecular sieve is a regular hexagonal molecular sieve with an a-axis length of 60-100 nm, a b-axis length of 50-70 nm, and a c-axis length of 100-150 nm; the tetrapropylammonium content Y in the Silicate-1 seed crystal is 0 < Y ≤ 11%.

[0061] In this application, when the tetrapropylammonium content Y in the Silicate-1 seed crystal is controlled to be 0 < Y ≤ 11%, the prepared ZSM-5 molecular sieve is a regular hexagonal molecular sieve with an a-axis length of 60-100 nm, a b-axis length of 50-70 nm, and a c-axis length of 100-150 nm, which can precisely control the size and morphology of the molecular sieve.

[0062] In some embodiments of this application, the ZSM-5 molecular sieve is a nanosheet layered molecular sieve with an a-axis length of 80-160 nm, a b-axis length of 10-50 nm, and a c-axis length of 200-700 nm; the tetrapropylammonium content Z in the Silicate-1 seed crystal is 0%.

[0063] In this application, when the tetrapropylammonium content Z in the Silicate-1 seed crystal is controlled to be 0%, the prepared ZSM-5 molecular sieve is a nanosheet layered molecular sieve with an a-axis length of 80-160 nm, a b-axis length of 10-50 nm, and a c-axis length of 200-700 nm, which can precisely control the size and morphology of the molecular sieve.

[0064] In some embodiments of this application, the Silicate-1 seed crystal is obtained from Silicate-1 seed mother liquor. The Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation, washing, redispersing, drying, and calcination to obtain Silicate-1 seed crystal with a tetrapropylammonium content of 0-40%.

[0065] In this application, Silicate-1 seed crystals are obtained from Silicate-1 seed mother liquor. The Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation, washing, redispersing, drying and calcination to obtain Silicate-1 seed crystals with a tetrapropylammonium content of 0-40%, which can then be used to prepare any one of spherical, regular hexagonal and nanosheet layered ZSM-5 molecular sieves.

[0066] In one embodiment, the tetrapropylammonium content X in the Silicate-1 seed mother liquor is 11% < X ≤ 40%. The Silicate-1 seed mother liquor is not treated in any way and is directly used as Silicate-1 seed in the preparation of ZSM-5 molecular sieve, which can produce spherical ZSM-5 molecular sieve with a particle size of 90-150 nm.

[0067] In another embodiment, the Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation and washing to obtain Silicate-1 seed crystals with a tetrapropylammonium content Y of 0 < Y ≤ 11%, which can be used to prepare regular hexagonal ZSM-5 molecular sieves with an a-axis length of 60-100 nm, a b-axis length of 50-70 nm, and a c-axis length of 100-150 nm.

[0068] In another embodiment, the Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation, washing, redispersing, drying, and calcination. The calcination temperature is 550-650℃, preferably 550℃, and the time is 4-12h, preferably 12h, to obtain Silicate-1 seed crystals with a tetrapropylammonium content Z of 0%. That is, after calcination, the tetrapropylammonium in the Silicate-1 seed crystals is completely removed, and nanosheet layered ZSM-5 molecular sieves with an a-axis length of 80-160nm, a b-axis length of 10-50nm, and a c-axis length of 200-700nm can be prepared.

[0069] In this application, Silicate-1 seed crystals with a tetrapropylammonium content of 0-40% are obtained by post-processing the Silicate-1 seed mother liquor, including centrifugation, washing, redispersing, drying and calcination. By gradually reducing the tetrapropylammonium content in the Silicate-1 seed crystals, the growth mechanism of ZSM-5 molecular sieve during the synthesis process is changed from 3D to 2D, and the morphology of the nano molecular sieve is changed from spherical to nanosheet structure.

[0070] In some embodiments of this application, the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel is 1:0.00025-0.05:0.08-1:10-120:0.001-0.5; and / or,

[0071] The first aging treatment is performed at a temperature of 30-100℃ for a time of 6-12 hours; and / or,

[0072] The temperature of the first crystallization treatment is 120-180℃, and the time is 12-48h.

[0073] This application specifies that the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel is 1:0.00025-0.05:0.08-1:10-120:0.001-0.5, preferably 1:0.025:0.35:60:0.1. The alkali-silica ratio in the first gel system can be adjusted to 0.08-1, preferably 0.4; the water-silica ratio is 10-120. The alkali-silica ratio has a significant impact on the a-axis and c-axis lengths of the synthesized nano-ZSM-5 molecular sieve; the water-silica ratio has a significant impact on the b-axis and c-axis lengths of the synthesized ZSM-5 molecular sieve.

[0074] In this application, the temperature of the first aging treatment is defined as 30-100℃, preferably 60℃; and the time is 6-12h, preferably 12h.

[0075] In this application, the temperature of the first crystallization treatment is defined as 120-180℃, preferably 140℃; the time is 12-48h, preferably 48h. The first crystallization treatment process can be at least one of solid-state crystallization, vapor-assisted crystallization, and atmospheric pressure rotary crystallization, preferably atmospheric pressure rotary crystallization.

[0076] This application limits the molar ratio between the components in the first gel and the temperature and time of the first aging treatment and the first crystallization treatment, so that the alkali-silicon ratio and water-silicon ratio in the first gel system are within a suitable range, so that the synthesized ZSM-5 molecular sieve has a suitable morphology and size.

[0077] In some embodiments of this application, the Silicate-1 seed solution is prepared by a method comprising the following steps:

[0078] 1) The system, including silicon source, alkaline solution, organic template agent and water, is subjected to hydrolysis to obtain a second gel;

[0079] 2) The second gel is subjected to a second aging treatment and a second crystallization treatment to obtain the Silicate-1 seed mother liquor.

[0080] In this application, a second gel is obtained by hydrolyzing the raw material system, and the second gel is subjected to a second aging treatment and a second crystallization treatment to obtain Silicate-1 seed mother liquor.

[0081] Specifically, in step 1), the system comprising a silicon source, an alkaline solution, an organic template agent, and water is hydrolyzed to obtain a second gel. The silicon source can be at least one of tetraethyl orthosilicate, silica sol, silicic acid, and water glass, preferably tetraethyl orthosilicate. The organic template agent can be at least one of tetrapropylammonium hydroxide and tetrapropylammonium bromide. The alkaline solution can be sodium hydroxide.

[0082] In step 2), the second gel undergoes a second aging treatment and a second crystallization treatment to obtain the Silicate-1 seed mother liquor. This application does not limit the temperature and time of the second aging treatment and the second crystallization treatment, as long as the Silicate-1 seed mother liquor can be obtained.

[0083] The preparation method provided in this application can prepare Silicate-1 seed mother liquor, and the process is simple and low in cost.

[0084] In some embodiments of this application, the molar ratio of silicon dioxide in the silicon source, hydroxide ions in the alkaline solution, organic template agent, and water is 1:0.01-1:0.01-1:4-100; and / or,

[0085] The second aging treatment is performed at a temperature of 30-80℃ for 1-7 days; and / or,

[0086] The second crystallization treatment is carried out at a temperature of 100-170℃ for 12-24 hours.

[0087] This application specifies that the molar ratio of silicon source, hydroxide ions in alkaline solution, organic template agent, and water is 1:0.01-1:0.01-1:4-100, preferably 1:0.35:0.35:12. This results in a water-silicon ratio of 4-100 in the second gel system, for example, 6.4, 9.2, or 19.2. Furthermore, the pH value of the second gel system is 7-14, preferably 9.

[0088] The temperature and time of the second aging treatment during the synthesis of Silicate-1 seed mother liquor have a significant impact on the final Silicate-1 seed particle size. Controlling the temperature and time of the second aging treatment allows for precise regulation of the solution supersaturation and the growth process of the Silicate-1 seed precursor. Specifically, the temperature of the second aging treatment is 30-80℃, preferably 30℃; the duration of the second aging treatment is 1-7 days, preferably 7 days. The aging method can be at least one of oil bath, water bath, or reactor aging, preferably reactor aging.

[0089] The second crystallization treatment is carried out at a temperature of 100-170℃ for 12-24 hours, which can enable the crystal nuclei to form an MFI structure and regulate the crystallinity and conversion rate of Silicate-1 seed crystals. The second crystallization treatment process can be at least one of solid-phase crystallization, steam-assisted crystallization, and atmospheric pressure rotation crystallization. Preferably, it can be atmospheric pressure rotation crystallization.

[0090] This application limits the molar ratio between the raw materials in the Silicate-1 seed mother liquor and the temperature and time of the second aging treatment and the second crystallization treatment, which can keep the water-silica ratio and pH value in the second gel system within a suitable range, and further enable the Silicate-1 seed crystals to have a suitable size, which is beneficial to controlling the morphology and size of the finally synthesized ZSM-5 molecular sieve.

[0091] In some embodiments of this application, the product of the second aging treatment is further subjected to a cooling treatment at 0-20°C.

[0092] In this application, the product of the second aging treatment is cooled at 0-20°C. Specifically, the product obtained from the second aging treatment can be placed in a reaction vessel, and the reaction vessel can be rinsed in cold water at 0-20°C until the temperature of the product of the second aging treatment drops to 0-20°C. This can reduce the supersaturation of the solute in the solution, further increase the number of crystal nuclei and reduce the size of the crystal nuclei.

[0093] The technical solution of this application will be further described below with reference to specific embodiments.

[0094] Example 1

[0095] The preparation method of ZSM-5 molecular sieve in this embodiment includes the following steps:

[0096] 1) Tetraethyl orthosilicate solution (AR, TEOS) and sodium hydroxide solution were slowly added to tetrapropylammonium hydroxide solution (25%, TPAOH) under stirring. The molar ratio of silicon dioxide in tetraethyl orthosilicate, hydroxide ions in sodium hydroxide, tetrapropylammonium hydroxide, and water was 1:0.2:0.35:12, denoted as ratio 1. The solution was then stirred at room temperature for 12 hours to allow complete hydrolysis of tetraethyl orthosilicate, yielding a second gel. Subsequently, under static conditions, the gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and aged at 60°C for 6 days. The reactor was immediately removed and rinsed with 10°C cold water for rapid cooling. After cooling to 10°C, the reactor was returned to a 100°C oven for a second crystallization treatment for 12 hours, yielding Silicate-1 seed mother liquor S-1. The average particle size of S-1 seed crystals was 30 nm.

[0097] 2) Silica sol (40%) was slowly added to NaOH solution (20wt%) under stirring. After magnetic stirring at room temperature for 12 hours, a clear and transparent solution was obtained. Al2(SO4)3 solution (13.2wt%) and water were then added, and the mixture was stirred at 25°C for 2 hours to obtain the second system. The Silicate-1 seed mother liquor S-1 (tetrapropylammonium (TPA) content of 40%) was directly added to the second system to obtain the first gel. The first gel contained silica sol (40%). The molar ratio of silicon dioxide, aluminum oxide, hydroxide, water, and Silicate-1 seed crystals was 1:0.025:0.4:30:0.05, denoted as ratio 2. After a first aging treatment of 6 hours with stirring at 30°C, the mixture was then transferred to a stainless steel reactor with a polytetrafluoroethylene liner under static conditions and subjected to rotary crystallization (first crystallization) at 170°C for 48 hours at a rotation speed of 40 rpm to obtain ZSM-5 molecular sieve (Na type), named Z-1(30). Z-1(30) is a spherical molecular sieve with a particle size of 90 nm. The Na type ZSM-5 molecular sieve was placed in a 1 mol / L ammonium chloride solution, and ammonium exchange was carried out at 80°C with stirring for 3 hours at a ratio of 1.0 g ZSM-5 molecular sieve to 50 mL ammonium chloride solution. The ammonium exchange step was repeated 3 times. After ammonium exchange, the sample was filtered, washed, and then placed in a muffle furnace for calcination at 550℃ for 4 hours. HZSM-5 molecular sieve was obtained after calcination.

[0098] Example 2

[0099] The preparation method of ZSM-5 molecular sieve in Example 2 is basically the same as that in Example 1, except that in step 2), 15g of S-1 is centrifuged, washed, dried, and then redispersed in 40g of deionized water. The content of tetrapropylammonium (TPA) in the dry Silicate-1 seed crystal is 11%. Then it is added to the second system to obtain the first gel in which the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystal is 1:0.025:0.4:30:0.05. The obtained ZSM-5 molecular sieve is named Z-2(30). Z-2(30) is a regular hexagonal molecular sieve with an a-axis length of 80nm, a b-axis length of 50nm, and a c-axis length of 100nm.

[0100] Example 3

[0101] The preparation method of ZSM-5 molecular sieve in Example 3 is basically the same as that in Example 1, except that in step 2), a certain amount of dry-based seed crystals obtained after centrifugation, washing and drying of S-1 are placed in a muffle furnace and heated to 550℃ at a rate of 2℃ / min, and calcined at a constant temperature for 12h to obtain calcined dry-based seed crystals. 0.3g of dry-based calcined seed crystals are added to 40g of deionized water, wherein the content of tetrapropylammonium (TPA) is 0%, and then added to the second system to obtain the first gel in which the molar ratio of silica, alumina, hydroxide, water and Silicate-1 seed crystals is 1:0.025:0.4:30:0.05. The obtained ZSM-5 molecular sieve is named Z-3(30). Among them, Z-3(30) is a nanosheet layered molecular sieve with an a-axis length of 80nm, a b-axis length of 40nm and a c-axis length of 225nm.

[0102] Example 4

[0103] The preparation method of ZSM-5 molecular sieve in Example 4 is basically the same as that in Example 3, except that the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel obtained in step 2) is 1:0.025:0.2:30:0.05. The resulting ZSM-5 molecular sieve is named Z-3-0.2. Z-3-0.2 is a nanosheet layered molecular sieve with an a-axis length of 115 nm, a b-axis length of 20 nm, and a c-axis length of 650 nm.

[0104] Example 5

[0105] The preparation method of ZSM-5 molecular sieve in Example 5 is basically the same as that in Example 3, except that the molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel obtained in step 2) is 1:0.025:0.5:30:0.05. The resulting ZSM-5 molecular sieve is named Z-3-0.5. Z-3-0.5 is a nanosheet layered molecular sieve with an a-axis length of 90 nm, a b-axis length of 30 nm, and a c-axis length of 220 nm.

[0106] Examples 6-18

[0107] The preparation methods of ZSM-5 molecular sieves in Examples 6-18 are basically the same as those in Example 3, except that one or more steps in the preparation method are changed. Specific parameters are shown in Tables 1-2.

[0108] Comparative Example 1

[0109] The preparation method of this comparative example is basically the same as that of the ZSM-5 molecular sieve in Example 1, except that Silicate-1 seed crystals were not added to the second system in step 2). Specific parameters are shown in Table 1-2.

[0110] Comparative Example 2

[0111] The preparation method of the ZSM-5 molecular sieve in this comparative example includes the following steps:

[0112] 1) Add 50g tetraethyl orthosilicate, 30g pure water, 2.63g sodium hydroxide, and 43.75g tetrapropylammonium hydroxide (40wt% aqueous solution) to a 200mL beaker. Stir at 35℃ for 2 hours, then raise the temperature to 45℃ and stir for 1 hour to form a homogeneous solution. Place the solution in a polytetrafluoroethylene liner and then into a high-pressure stainless steel hydrothermal reactor. Place the high-pressure reactor in a 100℃ oven for constant temperature crystallization for 12 hours. After crystallization, collect the resulting suspension directly and use it as the Silicate-1 seed suspension.

[0113] 2) Weigh 0.75g sodium hydroxide and 0.031g sodium aluminate into a 200mL beaker, then add 19.97g tetrapropylammonium bromide (TPABr), 1.389g ammonium fluoride, 20mL pure water, and 0.78g Silicate-1 seed suspension. Stir at room temperature for 1h to fully dissolve, obtaining solution A. Dissolve 15g silica sol (30wt%) in 30g pure water to obtain solution B. Add solution A to solution B to obtain the precursor solution. Place the precursor solution in a glass reactor and stir at 35℃ for 1h, then raise the temperature to 80℃ and stir for 1h. Filter once using a membrane filter press to obtain a dry gel product. Place the obtained dry gel in a polytetrafluoroethylene beaker, then place it in a high-pressure stainless steel hydrothermal reactor containing 50mL pure water and seal. Place the high-pressure reactor in a homogeneous reactor at 170℃ and allow it to crystallize for 12h. After crystallization, the precipitate was removed, filtered until neutral, and then calcined in a muffle furnace at 600℃ for 8 hours. After calcination, the obtained Na-type ZSM-5 molecular sieve was placed in a 1 mol / L ammonium chloride solution, and ammonium exchange was performed at a ratio of 1.0 g ZSM-5 molecular sieve to 50 mL ammonium chloride solution, stirred in an 80℃ water bath for 3 hours. The ammonium exchange step was repeated three times. After ammonium exchange, the sieve was filtered, washed, and then calcined in a muffle furnace at 550℃ for 4 hours. Short b-axis HZSM-5 molecular sieve was obtained after calcination. Specific parameters are shown in Table 1-2.

[0114] Comparative Example 3

[0115] The preparation method of the ZSM-5 molecular sieve in this comparative example includes the following steps:

[0116] 1) The all-silica molecular sieve Silicate-1 was synthesized using a pre-crystallization method with a feed ratio of 30SiO2:9TPAOH:900H2O. Specifically, 32.4g of ultrapure water and 9.15g of TPAOH (40wt%) were added to a 200ml beaker, and 12.5g of TEOS solution was slowly added dropwise while stirring. The mixture was stirred in an 80℃ water bath for 2 hours until the alcohol was almost completely evaporated, and water was added to the initial mass. The mixture was then transferred to a polytetrafluoroethylene reactor and statically crystallized at 100℃ for 72 hours. The resulting mother liquor was centrifuged, washed three times, and dried at 110℃ for 12 hours. Finally, it was calcined in a muffle furnace at 550℃ for 6 hours to obtain the all-silica molecular sieve Silicalite-1.

[0117] 2) Using Silicalite-1 molecular sieve as seed crystals at a dosage of 5 wt%, a pre-crystallization method was employed with seed crystal assistance. The feed ratio was 30SiO2:1Al:6TPAOH:900H2O. Specifically, 32.4 g of ultrapure water, 6.1 g of TPAOH (40 wt%), 0.248 g of NaAlO2 (Al2O3 content 41%), and 0.18 g of Silicalite-1 were added to a 200 ml beaker. While stirring, 11.875 g of TEOS solution was slowly added dropwise. The mixture was stirred in an 80°C water bath for 2 hours until the alcohol was almost completely evaporated, and water was added to the initial mass. The mixture was then transferred to a polytetrafluoroethylene reactor and statically crystallized at 170°C for 72 hours. The resulting mother liquor was centrifuged, washed three times, and dried at 110°C for 12 hours. After drying, the sample was calcined in a muffle furnace at 550℃ for 6 hours. The resulting sample was then subjected to ammonia exchange with 1M NH4Cl for 24 hours. After the exchange, the sample was calcined in a muffle furnace at 550℃ for 6 hours to obtain nano-sized HZSM-5.

[0118] 3) A certain concentration of zinc nitrate solution (Zn(NO3)2) was used to impregnate an equal amount of the catalyst to prepare 2wt% Zn / HZSM-5. The impregnated catalyst was dried at 110℃ for 12h and calcined in a muffle furnace at 550℃ for 6h to obtain ZSM-5 molecular sieve.

[0119] Figure 1 is a SEM image of the Silicate-1 seed crystals prepared in Example 1 of this application;

[0120] As can be seen from Figure 1, the Silicate-1 seed crystals prepared in Example 1 of this application have a small particle size, with a seed crystal size between 20-30 nm.

[0121] Figure 2 is a SEM image of the Silicate-1 seed crystals prepared in Comparative Example 2 of this application;

[0122] As can be seen from Figure 2, the Silicate-1 seed crystals prepared in Comparative Example 2 of this application have a larger particle size, with the seed crystal size between 30-50 nm.

[0123] Figure 3 is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 2 of this application;

[0124] As can be seen from Figure 3, the ZSM-5 molecular sieve prepared in Comparative Example 2 of this application has a b-axis of approximately 80 nm, an a-axis of 190 nm, and a c-axis of 270 nm, with a low aspect ratio of around 6.

[0125] Figure 4 is a SEM image of the spherical ZSM-5 molecular sieve prepared in Example 1 of this application;

[0126] As can be seen from Figure 4, the spherical ZSM-5 molecular sieve prepared in Example 1 of this application has a smaller particle size, with an average particle size of 90 nm, and a more regular shape.

[0127] Figure 5 is a SEM image of the regular hexagonal ZSM-5 molecular sieve prepared in Example 2 of this application;

[0128] As can be seen from Figure 5, the regular hexagonal ZSM-5 molecular sieve prepared in Example 2 of this application has a b-axis of 50 nm, an a-axis of 80 nm, and a c-axis of 100 nm, and its shape is more regular.

[0129] Figure 6 is a SEM image of the nanosheet-layered ZSM-5 molecular sieve prepared in Example 3 of this application;

[0130] As can be seen from Figure 6, the nanosheet-like ZSM-5 molecular sieve prepared in Example 3 of this application has a shorter b-axis (40 nm), an a-axis (80 nm), and a c-axis (225 nm), and its shape is more regular.

[0131] Figure 7 is a TEM image of the nanosheet-like ZSM-5 molecular sieve prepared in Example 3 of this application;

[0132] As can be seen from Figure 7, the nanosheet-like ZSM-5 molecular sieve prepared in Example 3 of this application has low axial lengths and pore-like defects on the surface of the molecular sieve b-axis. This is because the stability of the seed crystal structure decreases after the seed crystal is calcined to remove the internal TPA, resulting in dissolution behavior during the synthesis process.

[0133] Figure 8 is a SEM image of the nanosheet-layered ZSM-5 molecular sieve prepared in Example 4 of this application;

[0134] As can be seen from Figure 8, the nanosheet-like ZSM-5 molecular sieve prepared in Example 4 of this application has a shorter b-axis (15 nm), an a-axis (115 nm), and a c-axis (650 nm).

[0135] Figure 9 is a TEM image of the nanosheet-like ZSM-5 molecular sieve prepared in Example 5 of this application;

[0136] As can be seen from Figure 9, the nanosheet-like ZSM-5 molecular sieve prepared in Example 5 of this application has a shorter b-axis (30 nm), an a-axis (90 nm), and a c-axis (220 nm).

[0137] Figure 10 is a TEM image of the nanosheet-like ZSM-5 molecular sieve prepared in Example 5 of this application;

[0138] As can be seen from Figure 10, no porous defects appeared on the surface of the nanosheet-like ZSM-5 molecular sieve prepared in Example 5 of this application. This is because the silicon-base ratio was reduced during the synthesis process, and the seed crystals did not dissolve during the synthesis process.

[0139] Figure 11 shows the XRD patterns of the ZSM-5 molecular sieves prepared in Examples 1-3 and Comparative Examples 1-2 of this application;

[0140] As can be seen from Figure 11, the characteristic peaks of the ZSM-5 molecular sieves prepared in Examples 1-3 and Comparative Examples 1-2 of this application are basically consistent in the XRD spectra.

[0141] Figure 12 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 1 of this application in a scanning electron microscope;

[0142] Figure 13 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 2 of this application in a scanning electron microscope;

[0143] Figure 14 shows the mapping pattern of the ZSM-5 molecular sieve prepared in Example 3 of this application in a scanning electron microscope;

[0144] As can be seen from Figures 12-14, the silicon-aluminum ratios of the three ZSM-5 molecular sieves with different morphologies prepared in the embodiments of this application are the same, and the actual measured values ​​are 26, 18 and 17, respectively. Therefore, as the TPA content in Silicate-1 seed crystals decreases, the silicon-aluminum ratio of the ZSM-5 molecular sieves actually synthesized also decreases.

[0145] Figure 15 shows the physical adsorption curves of the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 of this application;

[0146] As can be seen from Figure 15, the micropore volume of the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 of this application is 0.15 cm³. 3 The crystallinity is around 0.28 cm³ / g, and the mesopore volume increases significantly with decreasing TPA content in Silicate-1 seed crystals, from 0.28 cm³ / g. 2 / g rose to 0.46cm 2 / g.

[0147] Figure 16 shows the pore size distribution of the ZSM-5 molecular sieves prepared in Examples 1, 2, and 3 of this application.

[0148] As can be seen from Figure 16, the ZSM-5 molecular sieves prepared in Examples 1, 2 and 3 of this application show a significant increase in the number of pores after the pore size of 60 nm, which should be attributed to intergranular packing pores.

[0149] Table 1

[0150] Table 2

[0151] As shown in Tables 1-2, compared with the comparative example, the ZSM-5 molecular sieve preparation method provided in this application can achieve the preparation of ZSM-5 molecular sieves with different morphologies by adjusting the content of tetrapropylammonium in Silicate-1 seed crystals. The ZSM-5 molecular sieves prepared by this method have smaller particle sizes, do not require the addition of template agents, have low cost, are simple to operate, and the generated wastewater is easy to treat, which is conducive to realizing large-scale industrial production.

[0152] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the ZSM-5 molecular sieve prepared by the method of this application has a smaller particle size, does not require the addition of template agent, has low cost, is simple to operate, and the wastewater generated is easy to treat, which is conducive to realizing large-scale industrial production.

[0153] Evaluation of the catalytic performance of ZSM-5 molecular sieve: Kaolin, binder, H-ZSM-5 molecular sieve, and REY molecular sieve were prepared according to a specific ratio and process to obtain the corresponding catalytic cracking catalyst. The reaction performance was evaluated using a small-scale fixed fluidized bed reactor. The feedstock oils used were Xinjiang vacuum wide-fraction wax oil and Xinjiang vacuum residue oil, with a residue blending ratio of 30%. The properties of the feedstock oils are shown in Table 3.

[0154] Table 3 Properties of feedstock oils used for catalyst selectivity assessment

[0155] The reaction performance of the HZSM-5 molecular sieve catalyst prepared in Example 3 and the HZSM-5 molecular sieve prepared in Comparative Example 2 was evaluated, and the results are listed in Table 4.

[0156] Table 4

[0157] As can be seen from Table 4, the ZSM-5 molecular sieve prepared by the method provided in this application can achieve a higher yield of propylene.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing ZSM-5 molecular sieve, characterized in that, Includes the following steps: 1) The first system, including silicon source and alkaline solution, is heated and stirred until it becomes clear. Then, aluminum source and water are added to the first system to obtain the second system. Silicate-1 seed crystals are added to the second system to obtain the first gel. The tetrapropylammonium content in the Silicate-1 seed crystal is 0-40%; 2) The first gel is subjected to a first aging treatment and a first crystallization treatment to obtain the ZSM-5 molecular sieve; The ZSM-5 molecular sieve is any one of spherical, regular hexagonal, or nanosheet layered molecular sieves.

2. The preparation method according to claim 1, characterized in that, The ZSM-5 molecular sieve is a spherical molecular sieve with a particle size of 90-150 nm; the tetrapropylammonium content X in the Silicate-1 seed crystal is 11% < X ≤ 40%.

3. The preparation method according to claim 1, characterized in that, The average particle size of the Silicate-1 seed crystal is 20-30 nm.

4. The preparation method according to claim 3, characterized in that, The ZSM-5 molecular sieve is a regular hexagonal molecular sieve with an a-axis length of 60-100 nm, a b-axis length of 50-70 nm, and a c-axis length of 100-150 nm; the tetrapropylammonium content Y in the Silicate-1 seed crystal is 0 < Y ≤ 11%.

5. The preparation method according to claim 3, characterized in that, The ZSM-5 molecular sieve is a nanosheet-like layered molecular sieve with an a-axis length of 80-160 nm, a b-axis length of 10-50 nm, and a c-axis length of 200-700 nm; the tetrapropylammonium content Z in the Silicate-1 seed crystal is 0%.

6. The preparation method according to any one of claims 1-5, characterized in that, The Silicate-1 seed crystals are obtained from Silicate-1 seed mother liquor. The Silicate-1 seed mother liquor is subjected to post-treatment including centrifugation, washing, redispersing, drying, and calcination to obtain Silicate-1 seed crystals with a tetrapropylammonium content of 0-40%.

7. The preparation method according to any one of claims 1-6, characterized in that, The molar ratio of silica, alumina, hydroxide, water, and Silicate-1 seed crystals in the first gel is 1:0.00025-0.05:0.08-1:10-120:0.001-0.5; and / or, The first aging treatment is performed at a temperature of 30-100℃ for a time of 6-12 hours; and / or, The temperature of the first crystallization treatment is 120-180℃, and the time is 12-48h.

8. The preparation method according to claim 6, characterized in that, The Silicate-1 seed solution is prepared by a method comprising the following steps: 1) The system, including silicon source, alkaline solution, organic template agent and water, is subjected to hydrolysis to obtain a second gel; 2) The second gel is subjected to a second aging treatment and a second crystallization treatment to obtain the Silicate-1 seed mother liquor.

9. The preparation method according to claim 8, characterized in that, The molar ratio of silicon dioxide in the silicon source, hydroxide ions in the alkaline solution, organic template agent, and water is 1:0.01-1:0.01-1:4-100; and / or, The second aging treatment is performed at a temperature of 30-80℃ for 1-7 days; and / or, The second crystallization treatment is carried out at a temperature of 100-170℃ for 12-24 hours.

10. The preparation method according to claim 8 or 9, characterized in that, Also includes: The product of the second aging treatment is cooled at 0-20°C.

Images