A process for the preparation of a low-silica zeolite

Abstract

The application provides a preparation method of low-silicon zeolite and relates to the technical field of zeolite materials. A silicon source, an aluminum source, an inorganic base, a template agent, water and zeolite seeds are mixed to obtain a gel; the gel is subjected to static hydrothermal reaction to obtain low-silicon zeolite; the low-silicon zeolite is low-silicon *MRE type zeolite or low-silicon MTT type zeolite. The low-silicon gel is guided and combined with seed assistance, and low-silicon *MRE zeolite and low-silicon MTT type zeolite are successfully synthesized. The obtained low-silicon *MRE zeolite and low-silicon MTT type zeolite all have extremely low silicon aluminum ratios, high purity and high crystallinity, wherein the silicon aluminum ratio of the low-silicon *MRE zeolite is as low as 5.2, and the silicon aluminum ratio of the low-silicon MTT type zeolite is as low as 12.

Description

Technical Field

[0001] This invention relates to the field of zeolite materials technology, and in particular to a method for preparing low-silica zeolite. Background Technology

[0002] *MRE-type zeolites (including ZSM-48, etc.) and MTT-type zeolites (including high-silica ZSM-23 and low-silica SSZ-32, etc.) both possess a one-dimensional straight-channel structure composed of 10-membered rings (*MRE-type zeolites) MTT type zeolite The unique pore structure endows *MRE and MTT type zeolites with important catalytic properties as acid catalysts. Like other one-dimensional zeolites (such as commercially available ZSM-22 and SAPO-11), *MRE and MTT type zeolites are suitable for industrially relevant hydroisomerization, a key process for enhancing the cold flow properties of fuels and lubricants.

[0003] The synthesis difficulty of zeolites with different topologies varies. Some topologies, such as Beta, ZSM-5, MOR, and CHA, are relatively easy to synthesize, with broad synthesis ligands (less prone to impurity phase formation) and a higher degree of crystallinity. However, the synthesis of MTT and *MRE topologies is relatively difficult. These zeolites have narrow synthesis phase regions and are prone to impurity phase formation. MTT synthesis easily generates ZSM-5 and CHA impurity phases, while *MRE synthesis easily generates α-alumina impurity phases. Currently, only the high-silicon, low-alumina type of these two zeolites can be produced using simple methods. However, the materials obtained by these methods have a low Brønsted acid site density, which is detrimental to catalytic reactions.

[0004] To date, the only feasible method for producing highly crystalline *MREs with a Si / Al ratio below 40 is to use diquaternary ammonium cationic pentabromium (PMBr2, (CH3)3N) + (CH2)5N + (CH3)3) as an organic structure-directing agent. The only feasible method for producing highly crystalline MTT with a Si / Al ratio below 20 is to use N,N′-diisopropylimidazolium hydroxide as a structure-directing agent. However, these methods involve the preparation of complex organic templates, which are too costly for industrial use. Although post-synthetic desilication methods have recently been developed, these methods are complex to operate. Currently, there are still technical bottlenecks in the synthesis of low-silicon*MRE and MTT-type zeolites using commercially available organic structure-directing agents. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preparing low-silica zeolite. The present invention can prepare *MRE-type zeolite and MTT-type zeolite with extremely low silica-alumina ratio, high purity and high crystallinity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing low-silica zeolite, comprising the following steps:

[0008] A gel is obtained by mixing silicon source, aluminum source, inorganic base, template agent, water and zeolite seed crystals;

[0009] The gel was subjected to a static hydrothermal reaction to obtain low-silica zeolite;

[0010] The low-silicon zeolite is a low-silicon *MRE type zeolite or a low-silicon MTT type zeolite; when the low-silicon zeolite is a low-silicon *MRE type zeolite, the template agent is one or more of hexamethylammonium bromide, hexamethyldiammonium hydroxide, and 1,6-hexanediamine, the zeolite seed crystal is a *MRE type zeolite seed crystal, and the molar ratio of effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(0.61~1.12):(1.13~2.08):(7.22~30.0):1.00:(2 28~785); When the low-silica zeolite is a low-silica MTT type zeolite, the template agent is one or more of isopropylamine, pyrrolidine and 1,4-butanediamine, the zeolite seed crystal is an MTT type zeolite seed crystal, and the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(1.98~3.62):(48.0~87.8):(23.9~43.8):1.00:(562~1562); M in M2O is a metal element in an inorganic alkali.

[0011] Preferably, the silicon source includes one or more of sodium silicate, silica fume, water glass, silica sol, and solid silica gel.

[0012] Preferably, the aluminum source includes one or more of sodium aluminate, boehmite, aluminum nitrate, aluminum sulfate, crystalline aluminum chloride, and aluminum hydroxide.

[0013] Preferably, the inorganic base includes one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0014] Preferably, when the low-silica zeolite is a low-silica *MRE type zeolite, the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O = (0.72~0.98):(1.33~1.80):(8.50~20.0):1.00:(325~604).

[0015] Preferably, the mass of the *MRE type zeolite seed crystal is 10% of the mass of SiO2 in the gel.

[0016] Preferably, when the low-silica zeolite is a low-silica MTT type zeolite, the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O = (2.33~3.15):(56.4~76.4):(28.1~38.1):1.00:(750~1250).

[0017] Preferably, the mass of the MTT-type zeolite seed crystal is 10% of the mass of SiO2 in the gel.

[0018] Preferably, the static hydrothermal reaction is carried out at a temperature of 150–250°C for 1–8 days.

[0019] Preferably, the silicon-to-aluminum molar ratio of the low-silicon *MRE type zeolite is 4 to 40, and the silicon-to-aluminum molar ratio of the low-silicon MTT type zeolite is 10 to 20.

[0020] This invention provides a method for preparing low-silicon zeolite, comprising the following steps: mixing a silicon source, an aluminum source, an inorganic base, a template agent, water, and zeolite seed crystals to obtain a gel; subjecting the gel to a static hydrothermal reaction to obtain low-silicon zeolite; wherein the low-silicon zeolite is a low-silicon *MRE type zeolite or a low-silicon MTT type zeolite; when the low-silicon zeolite is a low-silicon *MRE type zeolite, the template agent is one or more of hexamethylammonium bromide, hexamethyldiammonium hydroxide, and 1,6-hexamethylenediamine. The zeolite seed crystal is an *MRE type zeolite seed crystal, and the molar ratio of effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O = (0.61~1.12):(1.13~2.08):(7.22~30.0):1.00:(228~785); when the low-silica zeolite is a low-silica MTT type zeolite, the template agent is one or more of isopropylamine, pyrrolidine, and 1,4-butanediamine, the zeolite seed crystal is an MTT type zeolite seed crystal, and the molar ratio of effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O = (1.98~3.62):(48.0~87.8):(23.9~43.8):1.00:(562~1562); M in M2O is a metal element in an inorganic alkali. The silica-to-alumina ratio (S / A ratio) in the initial gel is correlated with that in the product. Low-silica zeolites generally originate from low-silica initial gels. However, when the S / A ratio in the gel is too low, impurity phases of other zeolites are easily generated, or even crystallization may occur. The seed-assisted synthesis method involves adding finished zeolites as seeds to the initial gel used for zeolite synthesis. Since the seed crystals have the same topological structure as the product, they can guide the crystallization process, increase the crystallinity of the zeolite, reduce the amount of template agent, and inhibit the formation of impurity phases. This invention combines low-silica gel guidance and seed-assisted synthesis to successfully synthesize low-silica *MRE zeolites and low-silica MTT-type zeolites. Both the obtained low-silica *MRE zeolites and low-silica MTT-type zeolites exhibit extremely low S / A ratios, high purity, and high crystallinity. The S / A ratio of the low-silica *MRE zeolite is as low as 5.2, and that of the low-silica MTT-type zeolite is as low as 12. Attached Figure Description

[0021] Figure 1 The X-ray powder diffraction patterns of zeolite products M1 to M6 in the examples are shown below.

[0022] Figure 2 This is a scanning electron microscope image of zeolite product M1 in Example 1;

[0023] Figure 3 This is a scanning electron microscope image of zeolite product M2 in Example 2;

[0024] Figure 4 This is a scanning electron microscope image of zeolite product M3 in Example 3;

[0025] Figure 5 This is a scanning electron microscope image of zeolite product M4 in Example 4;

[0026] Figure 6 This is a scanning electron microscope image of zeolite product M5 in Example 5;

[0027] Figure 7 This is a scanning electron microscope image of zeolite product M6 in Example 6;

[0028] Figure 8 The X-ray powder diffraction pattern of zeolite product C1 in Comparative Example 1;

[0029] Figure 9 The image shows a scanning electron microscope image of zeolite product C1 in Comparative Example 1.

[0030] Figure 10 The X-ray powder diffraction pattern of zeolite product C2 in Comparative Example 2;

[0031] Figure 11 The image shows a scanning electron microscope image of zeolite product C2 in Comparative Example 2.

[0032] Figure 12 The X-ray powder diffraction pattern of zeolite product C3 in Comparative Example 3;

[0033] Figure 13 X-ray powder diffraction pattern of zeolite product C4 in Comparative Example 4;

[0034] Figure 14 X-ray powder diffraction pattern of zeolite product C5 in Comparative Example 5;

[0035] Figure 15 X-ray powder diffraction pattern of zeolite product C6 in Comparative Example 6;

[0036] Figure 16 The X-ray powder diffraction pattern of zeolite product C7 in Comparative Example 7;

[0037] Figure 17 The image shows the X-ray powder diffraction pattern of zeolite product C8 in Comparative Example 8. Detailed Implementation

[0038] This invention provides a method for preparing low-silica zeolite, comprising the following steps:

[0039] A gel is obtained by mixing silicon source, aluminum source, inorganic base, template agent, water and zeolite seed crystals;

[0040] The gel was subjected to a static hydrothermal reaction to obtain low-silica zeolite;

[0041] The low-silicon zeolite is a low-silicon *MRE type zeolite or a low-silicon MTT type zeolite; when the low-silicon zeolite is a low-silicon *MRE type zeolite, the template agent is one or more of hexamethylammonium bromide, hexamethyldiammonium hydroxide, and 1,6-hexanediamine, the zeolite seed crystal is a *MRE type zeolite seed crystal, and the molar ratio of effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(0.61~1.12):(1.13~2.08):(7.22~30.0):1.00:(2 28~785); When the low-silica zeolite is a low-silica MTT type zeolite, the template agent is one or more of isopropylamine, pyrrolidine and 1,4-butanediamine, the zeolite seed crystal is an MTT type zeolite seed crystal, and the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(1.98~3.62):(48.0~87.8):(23.9~43.8):1.00:(562~1562); M in M2O is a metal element in an inorganic alkali.

[0042] Unless otherwise specified, all raw materials involved in this invention are commercially available products.

[0043] This invention mixes a silicon source, an aluminum source, an inorganic alkali, a template agent, water, and zeolite seed crystals to obtain a gel.

[0044] In this invention, the silicon source preferably includes one or more of sodium silicate, silica, water glass, silica sol, and solid silica gel, more preferably silica or silica sol. In this invention, the aluminum source preferably includes one or more of sodium aluminate, boehmite, aluminum nitrate, aluminum sulfate, crystalline aluminum chloride, and aluminum hydroxide, more preferably aluminum hydroxide or sodium aluminate. In this invention, the inorganic base preferably includes one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide, more preferably sodium hydroxide. In this invention, the water is preferably deionized water.

[0045] In this invention, when the low-silica zeolite is a low-silica *MRE type zeolite, the template agent is one or more of hexamethylammonium bromide, hexamethylbisammonium hydroxide, and 1,6-hexanediamine, more preferably hexamethylammonium bromide. The zeolite seed crystal is a *MRE type zeolite seed crystal. This invention does not have special requirements regarding the source of the *MRE type zeolite seed crystal, which can be obtained from commercially available products or prepared using methods well known to those skilled in the art. In an embodiment of this invention, the *MRE type zeolite seed crystal is prepared according to the following method:

[0046] 0.008 g aluminum hydroxide, 0.072 g sodium hydroxide and 5.4 mL distilled water were added to a reaction vessel and stirred evenly under sealed conditions at room temperature. 0.364 g hexamethylamine bromide was added, followed by 0.384 g silica. The mixture was crystallized at 190 °C for 5 days. The crystallized product was washed and dried at 100 °C for 1 day to obtain the *MRE type zeolite seed crystals.

[0047] In this invention, when the low-silica zeolite is a low-silica MTT-type zeolite, the template agent is one or more of isopropylamine, pyrrolidine, and 1,4-butanediamine, more preferably isopropylamine. The zeolite seed crystal is an MTT-type zeolite seed crystal. This invention does not have special requirements regarding the source of the MTT-type zeolite seed crystal, which can be obtained from commercially available products or prepared using methods well known to those skilled in the art. In an embodiment of this invention, the MTT-type zeolite seed crystal is prepared according to the following method:

[0048] 0.478 g sodium aluminate, 0.715 g sodium hydroxide and 101 mL distilled water were added to a reaction vessel and stirred evenly under sealed conditions at room temperature. 17.1 g isopropylamine was added, followed by 33.5 g silica sol (40%). The mixture was crystallized at 180 °C for 3 days. The crystallized product was washed and dried at 100 °C for 1 day to obtain the MTT type zeolite seed crystals.

[0049] In this invention, the preferred method for mixing the silicon source, aluminum source, inorganic alkali, template agent, water, and zeolite seed crystals is as follows:

[0050] The aluminum source, inorganic alkali and water are first stirred and mixed to obtain the first mixture;

[0051] After adding the template agent to the first mixture, a silicon source and zeolite seed crystals are added, and the mixture is stirred and mixed a second time to obtain the gel.

[0052] In this invention, the first stirring and the second stirring are preferably carried out under closed, room temperature conditions, and the first stirring and the second stirring are both aimed at mixing all components evenly.

[0053] In this invention, when the low-silica zeolite is a low-silica *MRE type zeolite, the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O = (0.61~1.12):(1.13~2.08):(7.22~30.0):1.00:(228~785), preferably (0.72~0.98):(1.33~1.80):(8.50~20.0):1.00:(325~604), and more preferably 0.85:1.57:15.0:1.00:465. The mass of the *MRE type zeolite seed crystal is preferably 10% of the mass of SiO2 in the gel.

[0054] In this invention, when the low-silica zeolite is a low-silica MTT-type zeolite, the molar ratio of the effective components in the gel is M2O:template:SiO2:Al2O3:H2O = (1.98~3.62):(48.0~87.8):(23.9~43.8):1.00:(562~1562), preferably (2.33~3.15):(56.4~76.4):(28.1~38.1):1.00:(750~1250), and more preferably 2.74:66.4:33.1:1.00:1000. The mass of the MTT-type zeolite seed crystals is preferably 10% of the mass of SiO2 in the gel.

[0055] In this invention, when calculating the molar ratio of effective components in the above-mentioned gel, the silicon source is calculated as SiO2, the aluminum source as Al2O3, and the inorganic base as M2O, where M is a metal element in the inorganic base; when the aluminum source is sodium aluminate, it is calculated as Na2O and Al2O3 (in this embodiment of the invention, sodium aluminate is calculated as 41wt% Na2O and 48wt% Al2O3).

[0056] After obtaining the gel, the gel of the present invention undergoes a static hydrothermal reaction to obtain low-silica zeolite.

[0057] In this invention, the temperature of the static hydrothermal reaction is preferably 150-250°C, more preferably 160-200°C, and even more preferably 170-190°C, and the time is preferably 1-8 days, more preferably 3-7 days, and even more preferably 4.5-5 days.

[0058] After the static hydrothermal reaction is completed, the product is preferably subjected to solid-liquid separation, solid phase washing, and drying in sequence to obtain the corresponding low-silica zeolite. In this invention, the solid-liquid separation method is preferably centrifugation, and the solid phase drying temperature is preferably 60-120°C, and the time is preferably 3-12 hours.

[0059] In this invention, the silicon-to-aluminum molar ratio of the low-silicon *MRE type zeolite is 4–40, and the silicon-to-aluminum molar ratio of the low-silicon MTT type zeolite is 10–20. In an embodiment of this invention, the silicon-to-aluminum molar ratio of the low-silicon *MRE type zeolite is 5.2–10.8, and the silicon-to-aluminum molar ratio of the low-silicon MTT type zeolite is 11.5–13.5.

[0060] This invention combines low-silicon gel guidance and seed crystal assistance to successfully synthesize low-silicon *MRE (ZSM-48) zeolite and low-silicon MTT (ZSM-23) type zeolite. The obtained low-silicon *MRE zeolite and low-silicon MTT type zeolite both have extremely low silicon-to-aluminum ratio, high purity and high crystallinity.

[0061] To further illustrate the present invention, the preparation method of the low-silica zeolite provided by the present invention will be described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0062] In each embodiment, the preparation method of *MRE type zeolite seed crystals is as follows: 0.008g aluminum hydroxide, 0.072g sodium hydroxide and 5.4mL distilled water are added to a reaction vessel and stirred evenly under sealed and room temperature conditions. 0.364g hexamethylamine bromide is added, followed by 0.384g silica. After crystallization at 190°C for 5 days, the crystallized product is washed and dried at 100°C for 1 day to obtain *MRE type zeolite seed crystals.

[0063] The preparation method of MTT-type zeolite seed crystals is as follows: 0.478g sodium aluminate, 0.715g sodium hydroxide and 101mL distilled water are added to a reaction vessel and stirred evenly under sealed and room temperature conditions. 17.1g isopropylamine is added, followed by 33.5g silica sol (40%). The mixture is crystallized at 180℃ for 3 days. After washing the crystallized product, it is dried at 100℃ for 1 day to obtain MTT-type zeolite seed crystals.

[0064] Example 1

[0065] Preparation of low-silica MRE type zeolites:

[0066] 0.0496 g of aluminum hydroxide, 0.0432 g of sodium hydroxide, and 5.4 mL of distilled water were added to a reaction vessel and stirred until homogeneous under sealed, room temperature conditions. Then, 0.364 g of hexamethylamine bromide was added, followed by 0.384 g of silica and 0.0382 g of *MRE type zeolite seed crystals. The mixture was stirred under sealed, room temperature conditions to form a homogeneous gel. The effective component composition and molar ratio were Na₂O:R:SiO₂:Al₂O₃:H₂O = 0.85:1.57:15.0:1.00:465 (R is the template agent hexamethylamine bromide). Static crystallization was carried out at 190 °C for 5 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 75 °C oven for 12 hours to obtain product M1. The Si / Al ratio of the product was determined and listed in Table 1.

[0067] Figure 1 Curve M1 in the diagram is the X-ray powder diffraction pattern of zeolite product M1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M1 is a zeolite with a *MRE structure. The Si / Al ratio of M1 was measured to be 5.2 by ICP.

[0068] Figure 2 The image shows a scanning electron microscope (SEM) image of zeolite product M1. The SEM image shows that the particle size of M1 is about 4 micrometers.

[0069] Example 2

[0070] 0.10 g aluminum hydroxide, 0.144 g sodium hydroxide, and 10.8 mL distilled water were added to a reaction vessel and stirred until homogeneous under sealed conditions at room temperature. 0.720 g hexamethylamine bromide was then added, followed by 0.780 g silica and 0.072 g *MRE type zeolite seed crystals. The mixture was stirred under sealed conditions at room temperature to form a homogeneous gel, which was then statically crystallized at 180 °C for 3 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 100 °C oven for 8 hours to obtain product M2. The Si / Al ratio of the product was determined and is listed in Table 1.

[0071] Figure 1 The medium curve M2 is the X-ray powder diffraction pattern of zeolite product M2. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M2 is a zeolite with a *MRE structure. The Si / Al ratio of M2 was measured to be 7.5 by ICP.

[0072] Figure 3 The image shows a scanning electron microscope (SEM) image of zeolite product M2. The SEM image shows that the particle size of M2 is about 4 micrometers.

[0073] Example 3

[0074] 0.21 g aluminum hydroxide, 0.12 g sodium hydroxide, and 15.2 mL distilled water were added to a reaction vessel and stirred thoroughly under sealed conditions at room temperature. 1.15 g hexamethylamine bromide was then added, followed by 1.13 g silica and 0.109 g *MRE type zeolite seed crystals. The mixture was stirred under sealed conditions at room temperature to form a homogeneous gel, which was then statically crystallized at 200 °C for 7 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 60 °C oven for 12 hours to obtain product M3. The Si / Al ratio of the product was determined and is listed in Table 1.

[0075] Figure 1 The curve M3 in the figure is the X-ray powder diffraction pattern of M3. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M3 is a zeolite with a *MRE structure. The Si / Al ratio of M3 was measured to be 10.8 by ICP.

[0076] Figure 4 This is a scanning electron microscope image of zeolite product M3. The particle size of M3 was observed to be around 3.5 micrometers.

[0077] Example 4

[0078] 2.3 g of sodium aluminate, 1.1 g of sodium hydroxide, and 160 mL of distilled water were added to a reaction vessel and stirred until homogeneous under sealed, room temperature conditions. 52 g of isopropylamine was then added, followed by 54 g of silica sol and 2.1 g of MTT-type zeolite seed crystals. The mixture was stirred under sealed, room temperature conditions to form a homogeneous gel. The effective component composition and molar ratio were Na₂O:R:SiO₂:Al₂O₃:H₂O = 2.72:53.0:33.0:1.00:1000 (R being the template agent isopropylamine). Static crystallization was carried out at 160 °C for 5 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 75 °C oven for 12 hours to obtain product M4. The Si / Al ratio of the product was determined and is listed in Table 1.

[0079] Figure 1 Curve M4 in the diagram is the X-ray powder diffraction pattern of zeolite product M4. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M4 is a zeolite with an MTT structure. The Si / Al ratio of M4 was measured to be 11.5 by ICP.

[0080] Figure 5 This is a scanning electron microscope image of zeolite product M4. The particle size of M4 was observed to be around 1 micrometer through scanning electron microscopy.

[0081] Example 5

[0082] 0.0384 g sodium aluminate, 0.0240 g sodium hydroxide, and 2.51 mL distilled water were added to a reaction vessel and stirred until homogeneous under sealed conditions at room temperature. 0.652 g isopropylamine was then added, followed by 0.825 g silica sol and 0.0330 g MTT-type zeolite seed crystals. The mixture was stirred under sealed conditions at room temperature to form a homogeneous gel, which was then statically crystallized at 170 °C for 3 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in an oven at 120 °C for 3 hours to obtain product M5. The Si / Al ratio of the product was determined and is listed in Table 1.

[0083] Figure 1 Curve M5 in the diagram is the X-ray powder diffraction pattern of zeolite product M5. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M5 is a zeolite with an MTT structure. The Si / Al ratio of M5 was measured to be 12.0 by ICP.

[0084] Figure 6 This is a scanning electron microscope image of zeolite product M5. The particle size of M5 was observed to be around 1 micrometer through scanning electron microscopy.

[0085] Example 6

[0086] 0.35 g sodium aluminate, 0.18 g sodium hydroxide, and 25 mL distilled water were added to a reaction vessel and stirred until homogeneous under sealed conditions at room temperature. 6.52 g isopropylamine was then added, followed by 8.2 g silica sol and 0.33 g MTT-type zeolite as seed crystals. The mixture was stirred under sealed conditions at room temperature to form a homogeneous gel, which was then statically crystallized at 175 °C for 4.5 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 100 °C oven for 9 hours to obtain product M6. The Si / Al ratio of the product was determined and is listed in Table 1.

[0087] Figure 1 The curve M6 in the diagram is the X-ray powder diffraction pattern of M6. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that M6 is a zeolite with an MTT structure. The Si / Al ratio of M6 was measured to be 13.5 by ICP.

[0088] Figure 7 This is a scanning electron microscope image of zeolite product M6. The particle size of M6 was observed to be around 1 micrometer through scanning electron microscopy.

[0089] Comparative Example 1

[0090] 0.072 g sodium hydroxide, 0.008 g aluminum hydroxide, and 5.4 mL distilled water were added to a reaction vessel and stirred until homogeneous under sealed conditions at room temperature. Then, 0.364 g hexamethylamine bromide was added, followed by 0.384 g silica. The mixture was stirred under sealed conditions at room temperature to form a homogeneous gel, which was then statically crystallized at 190 °C for 5 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 75 °C oven for 12 hours to obtain product Cl. The Si / Al ratio of the product was determined and is listed in Table 1.

[0091] Figure 8 This is the X-ray powder diffraction pattern of zeolite product C1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that C1 is a zeolite with a *MRE structure. The Si / Al ratio of C1 was measured to be 82 by ICP.

[0092] Figure 9 This is a scanning electron microscope image of zeolite product C1. The particle size of C1 was observed to be around 4 micrometers.

[0093] Comparative Example 2

[0094] 0.5 g sodium aluminate, 1.1 g sodium hydroxide, and 160 mL distilled water were added to a reaction vessel and stirred until homogeneous under sealed, room temperature conditions. 42 g isopropylamine was then added, followed by 54 g silica sol. The mixture was stirred under sealed, room temperature conditions to form a homogeneous gel, which was then statically crystallized at 160 °C for 5 days. After crystallization, solid-liquid separation was performed using a centrifuge. The solid product was dried in a 75 °C oven for 12 hours to obtain product C2. The Si / Al ratio of the product was determined and is listed in Table 1.

[0095] Figure 10 This is the X-ray powder diffraction pattern of zeolite product C2. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be determined that C2 is a zeolite with an MTT structure. The Si / Al ratio of C2 was measured to be 40 by ICP.

[0096] Figure 11 This is a scanning electron microscope image of zeolite product C2. The particle size of C2 was observed to be around 1 micrometer through scanning electron microscopy.

[0097] Table 1. Si / Al ratio of the zeolite products prepared in Examples 1-6 and Comparative Examples 1-2

[0098]

[0099] Comparative Example 3

[0100] Compared with Example 1, Comparative Example 3 did not add *MRE seed crystals, and all other conditions were the same as in Example 1, resulting in product C3.

[0101] Figure 12 This is the X-ray powder diffraction pattern of zeolite product C3. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C3 has a *MRE structure, but its crystallinity is extremely poor, making it unusable.

[0102] Comparative Example 4

[0103] Compared with Example 1, the crystallization temperature of Comparative Example 4 was 140°C, and all other conditions were the same as those in Example 1, resulting in product C4.

[0104] Figure 13 This is the X-ray powder diffraction pattern of zeolite product C4. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C4 does not have the *MRE structure.

[0105] Comparative Example 5

[0106] Compared with Example 1, Comparative Example 5 did not add hexamethylamine bromide, and all other conditions were the same as in Example 1, resulting in product C5.

[0107] Figure 14This is the X-ray powder diffraction pattern of zeolite product C5. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C5 does not have the *MRE structure.

[0108] Comparative Example 6

[0109] Compared with Example 4, Comparative Example 6 did not add MTT seeds, and all other conditions were the same as in Example 4, resulting in product C6.

[0110] Figure 15 This is the X-ray powder diffraction pattern of zeolite product C6. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C6 does not have an MTT structure.

[0111] Comparative Example 7

[0112] Compared with Example 4, the crystallization temperature of Comparative Example 7 was 100°C, and all other conditions were the same as those of Example 4, resulting in product C7.

[0113] Figure 16 This is the X-ray powder diffraction pattern of zeolite product C7. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C7 does not have an MTT structure.

[0114] Comparative Example 8

[0115] Compared with Example 4, Comparative Example 8 did not add isopropylamine, and all other conditions were the same as in Example 4, resulting in product C8.

[0116] Figure 17 This is the X-ray powder diffraction pattern of zeolite product C8. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, C8 does not have an MTT structure.

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-silica zeolite, characterized in that, Includes the following steps: A gel is obtained by mixing silicon source, aluminum source, inorganic base, template agent, water and zeolite seed crystals; The gel was subjected to a static hydrothermal reaction to obtain low-silica zeolite; The low-silicon zeolite is a low-silicon *MRE type zeolite or a low-silicon MTT type zeolite; when the low-silicon zeolite is a low-silicon *MRE type zeolite, the template agent is one or more of hexamethylammonium bromide, hexamethyldiammonium hydroxide, and 1,6-hexanediamine, the zeolite seed crystal is a *MRE type zeolite seed crystal, and the molar ratio of effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(0.61~1.12):(1.13~2.08):(7.22~30.0):1.00:(2 28~785); When the low-silica zeolite is a low-silica MTT type zeolite, the template agent is one or more of isopropylamine, pyrrolidine and 1,4-butanediamine, the zeolite seed crystal is an MTT type zeolite seed crystal, and the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(1.98~3.62):(48.0~87.8):(23.9~43.8):1.00:(562~1562); M in M2O is a metal element in the inorganic base; The silicon-to-aluminum molar ratio of the low-silicon *MRE type zeolite is 4~10.8, and the silicon-to-aluminum molar ratio of the low-silicon MTT type zeolite is 10~20; The static hydrothermal reaction is carried out at a temperature of 150~250℃ for 1~8 days.

2. The preparation method according to claim 1, characterized in that, The silicon source includes one or more of sodium silicate, silica fume, water glass, silica sol, and solid silica gel.

3. The preparation method according to claim 1, characterized in that, The aluminum source includes one or more of sodium aluminate, boehmite, aluminum nitrate, aluminum sulfate, crystalline aluminum chloride, and aluminum hydroxide.

4. The preparation method according to claim 1, characterized in that, The inorganic base includes one or more of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

5. The preparation method according to claim 1, characterized in that, When the low-silica zeolite is a low-silica *MRE type zeolite, the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(0.72~0.98):(1.33~1.80):(8.50~20.0):1.00:(325~604).

6. The preparation method according to claim 1 or 5, characterized in that, The mass of the *MRE type zeolite seed crystals is 10% of the mass of SiO2 in the gel.

7. The preparation method according to claim 1, characterized in that, When the low-silica zeolite is a low-silica MTT type zeolite, the molar ratio of the effective components in the gel is M2O:template agent:SiO2:Al2O3:H2O=(2.33~3.15):(56.4~76.4):(28.1~38.1):1.00:(750~1250).

8. The preparation method according to claim 1 or 7, characterized in that, The mass of the MTT-type zeolite seed crystals is 10% of the mass of SiO2 in the gel.

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