JP7676194B2 - Method for producing faujasite-type zeolite with high packing density - Google Patents

Description

The present invention relates to a method for producing faujasite-type zeolite with high packing density.

The substance zeolite is a general term for crystalline porous aluminosilicates. Zeolites have been widely used as catalysts, adsorbents, separation membranes, and other applications in many industrial processes, including oil refining and petrochemistry. For example, the fluid catalytic cracking process is an important process that uses a catalyst to crack the heavy oil in petroleum and obtain high-value-added fractions such as gasoline. Faujasite-type zeolite, a porous material with strong solid acidity, has long been used as a catalyst for this process. Faujasite-type zeolite has also long been used as an adsorbent.

In general, when zeolite is used as a catalyst or adsorbent, it is desirable to increase the packing density per unit volume and maximize the contact area per unit volume (Patent Document 1). As a method for solving this problem, a method is known in which primary particles of zeolite are aggregated to form spherical secondary particles (Patent Document 2). In this method, spherical secondary particles are formed by adding a binder component and spray drying. It is said that the packing density per unit volume can be increased by making the shape of the secondary particles spherical (Patent Document 1). This is because, while there are many gaps when irregular particles are packed, there are few unnecessary voids when spherical particles are packed, and the packing density can be increased because of excellent fluidity.

In this way, in the method of forming spherical secondary particles by spray drying, spherical secondary particles cannot be formed with zeolite alone, so a binder component is added. However, since components other than zeolite are included, there is an issue that the zeolite content is reduced.

Japanese Unexamined Patent Publication No. 59-137314 Japanese Unexamined Patent Publication No. 54-29898

The faujasite-type zeolite (hereinafter referred to as FAU-type zeolite) according to the production method of the present invention is not one in which secondary particles are made spherical as in the conventional method, but one in which the shape of primary particles is made close to spherical to increase the packing density. The present invention provides a method for producing such an FAU-type zeolite.

The present invention has solved the above-mentioned problems by the following configuration, and is a method for producing FAU type zeolite, comprising: a precursor preparation step of preparing an aqueous mixed solution containing a Si source, an Al source, and seed crystals; and a hydrothermal treatment step of hydrothermally treating the aqueous mixed solution to grow FAU type zeolite crystals, characterized in that silica particles having a specific surface area of 100 ^m2 /g or less are used as the Si source of the aqueous mixed solution containing the seed crystals.

The FAU zeolite produced by the production method of the present invention has many primary particles having a nearly spherical shape, so that it is possible to obtain a powder having a high zeolite content per unit volume.

Conceptual diagram of sphericity. Electron microscope photograph of the zeolite powder of Example 1. Electron microscope photograph of the zeolite powder of Comparative Example 1. Electron microscope photograph of the zeolite powder of Comparative Example 2. Electron microscope photograph of the zeolite powder of Comparative Example 3.

[FAU type zeolite]
The FAU zeolite according to the production method of the present invention (hereinafter referred to as the FAU zeolite of the present invention ) is an FAU zeolite having a shape close to a sphere with a sphericity of primary particles of 0.60 or more as determined by image analysis. The FAU zeolite has a faujasite structure with Si, Al, and O as basic skeletal elements, and this faujasite structure can be confirmed from a diffraction pattern obtained by X-ray diffraction measurement.

Conventional FAU zeolites have low packing density because they contain many octahedral or hexagonal plate-like primary particles with distinct crystal faces (Comparative Examples 1 and 4). In contrast, the FAU zeolite of the present invention contains many primary particles with high sphericity, and therefore has a higher packing density than conventional FAU zeolites. As shown in the following formula [1], when A is the area measured by image analysis of the zeolite primary particles and B is the area of a perfect circle whose diameter is the major axis of the primary particles measured by image analysis, the sphericity is expressed by the ratio of the measured area A to the area B of the perfect circle.
X=A/B...[1]
(In formula [1], X is the sphericity, A is the area measured by image analysis, and B is the area of a perfect circle whose major axis is the diameter measured by image analysis.)
The concept of sphericity is shown in Figure 1. The closer the sphericity is to 1.0, the closer it is to a perfect sphere.

The sphericity of the primary particles of the FAU zeolite of the present invention is 0.60 or more on average, preferably 0.65 or more, and more preferably 0.70 or more. The FAU zeolite of the present invention has primary particles with a sphericity close to that of a sphere, and the range of the sphericity of the primary particles is 0.60 or more and 1.0 or less.

The primary particle diameter of the FAU type zeolite of the present invention is preferably in the range of 0.1 μm to 10 μm, more preferably in the range of 0.5 μm to 5 μm, and particularly preferably in the range of 0.7 μm to 5 μm. When the primary particle diameter of the FAU type zeolite of the present invention is in these ranges, the packing density becomes higher. This primary particle diameter can be measured by image analysis.

The properties of the FAU zeolite of the present invention are greatly affected by the molar ratio of Si to Al ( _SiO2 / _{Al2O3 molar} ratio: SAR). For example, an FAU zeolite with a low SAR (high Al content) has a high solid acidity. In addition, the hydrothermal resistance is superior when the SAR is high (low Al content). The preferred SAR range varies depending on the application. For example, for use as a detergent builder or moisture adsorbent, an FAU zeolite with a low SAR is preferred, more preferably an SAR of less than 5, and particularly preferably an X-type zeolite with an SAR of less than 2. For use as a VOC adsorbent, an FAU zeolite with an SAR of 30 or more is preferred, and an FAU zeolite with an SAR of 50 or more is more preferred. For catalytic applications, FAU-type zeolite (Y-type zeolite) having an SAR of 5 or more is preferred, with an SAR in the range of 5 to 400 being more preferred, and 5 to 200 being particularly preferred.

The FAU zeolite of the present invention has a cation exchange site and can be ion-exchanged with various cations. For example, it can be exchanged with various cations such as alkali metals such as Na and K, transition metals, rare earths, protons, and ammonium ions, and the properties of the FAU zeolite change depending on the cations exchanged. For example, if it is used as a detergent or adsorbent, it is preferable that it is ion-exchanged with alkali metals such as Na and K. In addition, when it is used for a catalyst application in a reaction that utilizes its solid acidity, it is preferable that it is ion-exchanged with protons, and it is more preferable that the content of alkali that inhibits the expression of the solid acidity is small, and specifically, it is preferable that it is 2 mass% or less in terms of M ₂ O (M is an alkali metal), more preferably 1 mass% or less, and particularly preferably less than 0.5 mass%. Note that the packing density of the FAU zeolite also changes depending on the type of cation exchange site, so when confirming the effects of the present invention, the cations of the cation exchange sites were made the same in the examples and comparative examples for comparison.

The FAU zeolite of the present invention preferably has a specific surface area of 600 m ² /g or more. Zeolites generally have an extremely large specific surface area due to the pore structure derived from their skeleton. If the specific surface area of the FAU zeolite of the present invention is lower than 600 m ² /g, the pore structure derived from the skeleton may not be sufficiently developed, and the solid acidity may be low. The higher the specific surface area of the FAU zeolite, the more preferable it is, but the upper limit may be 900 m ² /g or less. More specifically, the specific surface area of the FAU zeolite of the present invention may be in the range of 650 m ² /g or more to 750 m ² /g or less.

The FAU zeolite of the present invention is processed into various forms depending on the application. When used as a detergent builder, it is used as is in powder form, and when used as an adsorbent, it is molded into pellets or tablets together with a binder component and used. When used as a catalyst, it is molded into spheres, pellets or tablets together with an active metal component, a cocatalyst component, a carrier component, a binder component, etc. and used. Specific examples of catalyst applications include use as a fluid catalytic cracking catalyst or hydrocracking catalyst in petroleum refining.

Since the FAU zeolite of the present invention has a high sphericity, the packing density can be increased. Specifically, for example, a packing density of more than 0.4 g/ ^cm3 to 0.6 g/ ^cm3 or less can be obtained. FAU zeolite with a high packing density is excellent in terms of transportation costs because a large amount of FAU zeolite is packed per unit volume. In addition, since the FAU zeolite of the present invention does not contain a binder component, the amount of FAU zeolite per unit volume can be increased compared to that of zeolite molded into spherical secondary particles by adding a binder component.

[Method for producing FAU type zeolite]
The method for producing the FAU zeolite of the present invention will now be described in detail.
The production method of the present invention is a production method for FAU type zeolite, and includes a precursor preparation step of preparing an aqueous mixed solution containing a Si source, an Al source, and FAU type zeolite seed crystals (hereinafter, may be simply referred to as seed crystals), and a hydrothermal treatment step of hydrothermally treating the aqueous mixed solution to grow FAU type zeolite crystals, characterized in that slowly soluble silica particles are used as the Si source of the aqueous mixed solution containing the seed crystals.

The aqueous mixture is prepared, for example, by adding slowly soluble silica particles, which are a Si source, and an Al source to a seed solution containing seed crystals. The slowly soluble silica particles are silica particles that dissolve slowly, and for example, silica particles with a specific surface area of 100 ^m2 /g or less are used. For example, silica fine powder with a specific surface area of 400 ^m2 /g or more is easily dissolved (easily soluble) and is not suitable as a Si source to be added to the seed solution.

FAU type zeolite is a type of crystalline aluminosilicate with Si, Al, and O as the basic skeletal elements, and raw materials containing Si (Si source) and Al (Al source) as the structural elements of the skeletal structure are used as raw materials. In the manufacturing method of the present invention, for example, an aqueous mixture is prepared by adding slowly soluble silica particles, which are a Si source, and an Al source to a seed solution containing the above-mentioned seed crystals, and the aqueous mixture is heated to grow FAU type zeolite crystals. It is known that FAU type zeolite crystals grow by repeated dissolution and reprecipitation of Si and Al in an aqueous solution. In the manufacturing method of the present invention, the rate of dissolution and reprecipitation of Si and Al is slowed down by using slowly soluble silica particles as a Si source for growing the seed crystals, and primary particles having a shape close to a sphere are grown, which is different from that of conventional FAU type zeolites.

[Precursor preparation step]
The production method of the present invention includes, for example, a precursor preparation step of preparing an aqueous mixture by adding slowly soluble silica particles, which are a Si source, and an Al source to a seed solution containing FAU type zeolite seed crystals. The solution containing the seed crystals can be prepared by aging an aqueous solution having the following molar composition. In the production method of the present invention, the aqueous solution containing the seed crystals is called a seed solution.
Na ₂ O/Al ₂ O ₃ =5 to 32
SiO ₂ /Al ₂ O ₃ =5 to 30
H ₂ O/Al ₂ O ₃ =100-2000

The Na source used in preparing the seed solution is NaOH, sodium silicate (water glass), sodium aluminate, etc. The Si source is silica sol, silica gel, alkoxysilane such as tetraalkoxysilane, water glass, etc. The Si source of this seed solution can be one that is easily dissolved (easily soluble). In terms of reactivity, water glass is preferred as this Si source. Note that water glass with a Na ₂ O/SiO ₂ molar ratio of 1 to 3.5 is usually used. The Al source is alumina sol, alumina gel, sodium aluminate, aluminum sulfate, etc. Of these, sodium aluminate is preferred in terms of reactivity with silica and crystallization.

The Na ₂ O/Al ₂ O ₃ molar ratio after mixing each raw material such as sodium aluminate, NaOH, and water glass is preferably in the range of 5 to 32, more preferably in the range of 8 to 24. When the Na ₂ O/Al ₂ O ₃ molar ratio is in this range, seed crystals are easily generated. The SiO ₂ /Al ₂ O ₃ molar ratio after mixing each raw material is preferably in the range of 5 to 30, more preferably in the range of 10 to 20. When the SiO ₂ /Al ₂ O ₃ molar ratio is less than 5, crystals other than FAU type zeolite such as P type zeolite and gmelinite may be mixed, and when the SiO ₂ /Al ₂ O ₃ molar ratio exceeds 30, it may be difficult to obtain FAU type zeolite crystals.

The H ₂ O/Al ₂ O ₃ molar ratio after mixing the above raw materials is preferably in the range of 100 to 2000, more preferably in the range of 150 to 1500. If the _{H 2} O/Al ₂ O ₃ molar ratio is less than 100, primary particles having an irregular shape are likely to be obtained. If the H ₂ O/Al ₂ O ₃ molar ratio exceeds 2000, primary particles tend to be octahedral or hexagonal plate-like, and it is difficult to obtain spherical particles.

A seed solution is obtained by aging the aqueous solution of the above raw materials at 10 to 70°C, preferably 20 to 50°C. The aging time varies depending on the aging temperature, but is usually 1 to 200 hours.

To the seed solution, slowly soluble silica particles as a Si source, an Al source, and water are added to prepare an aqueous mixture. As the slowly soluble silica particles as a Si source, for example, silica particles with a specific surface area of 100 ^m2 /g or less are used. Since silica particles with such a small specific surface area dissolve slowly (slow solubility), the dissolution and reprecipitation of Si and Al in the next step proceeds slowly, and primary particles (primary particles of FAU type zeolite crystals) that are nearly spherical are obtained. The above-mentioned compounds can be used as the Al source.

The molar composition of the aqueous mixture containing the Si source, Al source, and seed crystals is preferably in the following range: When the molar composition of the aqueous mixture is in this range, primary particles close to spheres are easily produced.
Na ₂ O/Al ₂ O ₃ =1 to 10
SiO ₂ /Al ₂ O ₃ =1 to 20
H ₂ O/Al ₂ O ₃ =50-600

The Na ₂ O/Al ₂ O ₃ molar ratio of the aqueous mixture is preferably in the range of 1 to 10, more preferably in the range of 1 to 5. The SiO ₂ /Al ₂ O ₃ molar ratio of the aqueous mixture is preferably in the range of 1 to 20, more preferably in the range of 1 to 10. Furthermore, the H ₂ O/Al ₂ O ₃ molar ratio of the aqueous mixture is preferably in the range of 50 to 600, more preferably in the range of 80 to 200. When the molar composition of the aqueous mixture is in these ranges, primary particles having a shape close to a sphere tend to grow.

As a precursor preparation process, a case was shown in which an aqueous mixture was prepared by adding slowly soluble silica particles, which are a Si source, and an Al source to a seed solution containing FAU-type zeolite seed crystals, but the preparation of the aqueous mixture is not limited to the method of adding slowly soluble silica particles, which are a Si source, and an Al source to a seed solution containing seed crystals.

[Hydrothermal treatment process]
In this step, the aqueous mixture obtained in the above-mentioned precursor preparation step is heat-treated to promote crystallization of the FAU-type zeolite.

The heat treatment may be carried out by a conventional method such as heat treatment under pressure using an autoclave or heat treatment under normal pressure. In the manufacturing method of the present invention, heat treatment under normal pressure is preferred from the viewpoint of slowing down the dissolution rate of the Si source.

The temperature of the heat treatment may be any temperature that promotes the crystallization of FAU-type zeolite, and is preferably 50°C to 100°C. If the heat treatment is performed under normal pressure, it is more preferable that the temperature be 80°C to 100°C. The time of the heat treatment depends on the heating temperature, but may be 2 to 200 hours.

[Other steps]
The production method of the present invention can include a step of removing the solvent from the solution containing FAU zeolite obtained in the crystallization step to separate the FAU zeolite. This can be easily carried out by a conventionally known method such as drying, centrifugation, or filtration.

The manufacturing method of the present invention may include a step of ion-exchanging FAU-type zeolite. Ion exchange can be easily performed by suspending FAU-type zeolite in an aqueous solution in which the cations to be exchanged are dissolved, and treating at an appropriate temperature for an appropriate time. Although it depends on the type of cation, the ion exchange temperature is preferably in the range of room temperature to 95°C, and the ion exchange time is preferably about 0.5 to 10 hours.

The production method of the present invention may include a dealumination step in order to increase the _SiO2 / _{Al2O3 molar} ratio of the FAU zeolite. The dealumination method may be a conventionally known method. For example, aluminum can be removed from the FAU zeolite by acid treatment, steam treatment, EDTA treatment, or other methods, and the _SiO2 / _{Al2O3 molar} ratio can be increased to about 200.

Below, examples of the present invention are shown together with comparative examples. Note that the present invention is not limited to the following examples. In the examples and comparative examples, physical properties such as specific surface area and chemical composition were measured by the following methods.

[Specific surface area]
The sample powder pretreated at 500°C for 1 hour under an inert gas atmosphere was filled into a sample tube, and the specific surface area of the sample powder was measured using a specific surface area measuring device ("MR-6" manufactured by Nippon Bell Co., Ltd.). Specifically, a mixed gas of nitrogen gas concentration 30 vol% and helium gas concentration 70 vol% was passed through a sample tube sufficiently cooled with liquid nitrogen to adsorb nitrogen to the sample powder, and the sample tube was then cooled to 25°C to detect the amount of nitrogen desorbed from the sample powder with a TCD detector. The amount of desorbed nitrogen was converted to a specific surface area using the cross-sectional area of the nitrogen molecule to calculate the specific surface area per gram of sample powder.

[Composition analysis]
The contents of Si, Al and alkali in the sample powder were measured using a fluorescent X-ray analyzer (RIX-3000). From the measurement results, the contents of Si and Al were converted into _SiO2 and _{Al2O3 molar} amounts, respectively, to calculate the _SiO2 / _{Al2O3 molar} ratio.

[Ignition loss]
The ignition loss was calculated from the weight loss observed when the sample powder was heated at 1000° C. for 1 hour using the following formula.
Ignition loss (%) = [(weight of sample powder before heating (g) - weight of sample powder after heating (g)] / weight of sample powder before heating (g)

[Sphericity of primary particles]
After dispersing the sample powder on a sample plate, the shape of the primary particles was observed using a scanning electron microscope (JEOL Ltd.: JSM-7600S) (accelerating voltage 1.0 kV, magnification 10,000 to 50,000 times). 50 primary particles were randomly selected from the obtained image, and the area of the primary particle measured by image analysis was taken as A, the area of the perfect circle with the diameter of the major axis of the primary particle measured by image analysis was taken as B, and the sphericity X was calculated using the following formula [1]. The primary particle diameter was taken as the average value of the major axes.
Sphericity of primary particles (X) = A/B... [1]

[Filling density]
The sample powder was filled into a 200 ml graduated cylinder up to the 100 ml mark, and then tapped up and down 100 times from a height of about 1 cm. The weight of the sample powder filled into the graduated cylinder was T (g), and the volume after tapping was V1 (cm ³ ), and the packing density (ρ) was calculated using the following formula [2].
Packing density (ρ) = T/V1 ...[2]

[X-ray diffraction measurement]
The sample powder was ground in a mortar and set on a sample plate. X-ray diffraction measurement was performed under the following conditions, and the presence or absence of a faujasite structure was confirmed from the obtained XRD pattern.
Equipment: Rigaku MiniFlex
Operation axis: 2θ/θ
Radiation source: CuKα
Measurement method: Continuous Voltage: 40 kV
Current: 15mA
Starting angle: 2θ=5°
End angle: 2θ=50°
Sampling width: 0.020°
Scan speed: 10.000 [°/min]
<Judgment criteria>
When the X-ray diffraction pattern obtained by the above measurement has all the peaks attributable to the Miller indices of the faujasite structure, it is judged that the faujasite structure is present. Note that the peak positions of the respective peaks may include an error of about 2θ=±0.2°.

Example 1
<Precursor Preparation Step>
0.29 kg of a sodium aluminate aqueous solution with a Na content ( _Na2O equivalent) of 17% by mass and _an Al content ( _Al2O3 equivalent) of 22% by mass was prepared. This sodium aluminate aqueous solution was added to 2.4 kg of a 21.7% by mass aqueous sodium hydroxide solution. This solution was added to 2.3 kg of No. 3 water glass with a Si concentration ( _SiO2 equivalent) of 24% by mass while stirring, and after stirring for 1 hour, the mixture was left to stand at 30°C for ₁₂ hours to prepare a seed solution. The molar composition of the seed solution was _16Na2O : _Al2O3 : _15SiO2 : _330H2O .

As the Si source, 18 kg of No. 3 water glass with a Si concentration ( _SiO2 equivalent) of 24 mass%, 4.5 kg of slowly soluble silica particles (fused silica UFP-30 manufactured by Denka Co., Ltd., specific surface area 37 ^m2 /g) and 16.8 kg of water were mixed. After adding 2.5 kg of the seed solution to this solution, 8.1 kg of sodium aluminate with a Na content ( _Na2O equivalent) of 7.7 mass% and _an Al content ( _Al2O3 equivalent) of 22 mass% was added as the _Al source to prepare an aqueous mixture. The molar composition of this aqueous mixture was _2.8Na2O : _Al2O3 : _8.6SiO2 : _113H2O .

<Hydrothermal treatment process>
The aqueous mixture was aged for 3 hours at room temperature, and then heat-treated at 95°C for 35 hours to grow zeolite crystals. The zeolite crystals were then filtered off, washed with water, and dried at 130°C for 20 hours. The obtained zeolite crystals were confirmed to have a faujasite structure by X-ray diffraction measurement. The above-mentioned measurements were also carried out. The results are shown in Table 1. An electron microscope photograph of this FAU-type zeolite is shown in Figure 2.

Example 2
5 kg of the FAU zeolite obtained in Example 1 was added to 50 L of water at 60°C, and 1.4 kg of ammonium sulfate was further added to prepare a suspension. This suspension was stirred at 70°C for 1 hour, and then the FAU zeolite was filtered off. This FAU zeolite was washed with water, then washed with an ammonium sulfate solution in which 1.4 kg of ammonium sulfate was dissolved in 50 L of water at 60°C, and further washed with 50 L of water at 60°C. The washed FAU zeolite was dried at 130°C for 20 hours to obtain FAU zeolite ion-exchanged with ammonium ions. The above-mentioned measurements were carried out on this FAU zeolite. The results are shown in Table 1.

Example 3
The FAU zeolite obtained in Example 2 was calcined at 670°C for 1 hour in a saturated steam atmosphere to perform the first steam treatment. 4.0 kg of this FAU zeolite was added to 400 L of water at 60°C, and then 5.6 kg of ammonium sulfate was added to prepare a suspension. This suspension was stirred at 90°C for 1 hour, and then the FAU zeolite was filtered out. This was washed with 240 L of water at 60°C and dried at 110°C for 20 hours to obtain FAU zeolite crystals with an increased _SiO2 / _{Al2O3 molar} ratio. Furthermore, this FAU zeolite crystal was calcined at 630°C for 2 hours in a saturated steam atmosphere to perform the second steam treatment. 1.0 kg of this FAU zeolite crystals was added to 15 L of water at room temperature, and 1.4 kg of 25% by mass sulfuric acid was gradually added. After the entire amount of sulfuric acid was added, the temperature was raised to 75° C. and the mixture was stirred for 4 hours, and the FAU zeolite was filtered and washed with 60 L of ion-exchanged water. The washed FAU zeolite was dried at 110° C. for 20 hours to obtain FAU zeolite crystals with a further increased SiO ₂ /Al ₂ O ₃ molar ratio. The above-mentioned measurements were carried out on this FAU zeolite crystal. The results are shown in Table 1.

[Comparative Example 1: Commercially available FAU type zeolite]
A commercially available FAU type zeolite (CBV100 manufactured by Zeolyst Co., Ltd.) was used. The above-mentioned measurements were carried out on this FAU type zeolite. The results are shown in Table 1. An electron microscope photograph of this FAU type zeolite is shown in Figure 3.

[Comparative Example 2: Use of easily soluble silica particles]
FAU zeolite was produced in the same manner as in Example 1, except that, as the Si source to be added to the seed solution, easily soluble silica particles were used instead of the slowly soluble silica. As the easily soluble silica particles, a product of Nippon Aerosil Co., Ltd. (Aerosil ^TM 380, specific surface area 405 ^m2 /g) was used. The above-mentioned measurements were carried out on this FAU zeolite. The results are shown in Table 1. An electron microscope photograph of this FAU zeolite is shown in Figure 4.

Comparative Example 3: Silica particles not added to the raw material solution
35 kg of No. 3 water glass with a Si concentration ( _SiO2 equivalent ₎ of 24% was slowly added to 7.4 kg of an aluminum sulfate aqueous solution with a _H2SO4 concentration of 20.3% by mass and an Al concentration ( _{Al2O3 equivalent} ) of 7.0% by mass, and then 5.3 kg of sodium aluminate with a Na content ( _{Na2O equivalent} ) of 7.7% by mass and an Al content ( _Al2O3 equivalent) of 22% by mass was added and stirred for 10 minutes to prepare a raw material solution. 2.4 kg of the seed solution obtained by the method of Example 1 was added to this raw material solution, and the mixture was stirred and mixed until it became uniform to prepare an aqueous mixture. The molar composition of this aqueous mixture was _2.8Na2O : _Al2O3 : _8.6SiO2 : _{113H2O .} The subsequent steps were performed in the same manner as in Example 1 to prepare FAU type zeolite. The above-mentioned measurements were performed on this FAU type zeolite. The results are shown in Table 1. An electron microscope photograph of this FAU zeolite is shown in FIG.

[Comparative Example 4: Commercially available FAU type zeolite]
A commercially available FAU type zeolite (CBV712 manufactured by Zeolyst Co., Ltd.) was used. The above-mentioned measurements were carried out on this FAU type zeolite. The results are shown in Table 1.

The FAU zeolite of Example 1, which was prepared using slowly soluble silica particles (specific surface area 37 m ² /g) as the Si source to be added to the seed solution, has mostly rounded primary particles (FIG. 2), with a sphericity of 0.75. On the other hand, the primary particles of the FAU zeolite of Comparative Example 2, which was prepared using easily soluble silica particles (specific surface area 405 m ² /g) instead of the slowly soluble silica particles, are mostly octahedral, with some hexagonal plate-shaped primary particles included (FIG. 4). The FAU zeolite of Comparative Example 3, which was prepared without using silica particles as the Si source to be added to the seed solution, has mostly hexagonal plate-shaped primary particles, with some octahedral primary particles included (FIG. 5). The commercially available FAU zeolite of Comparative Example 1 also contains primary particles with a shape similar to that of the FAU zeolite of Comparative Example 3 (FIG. 3). In this manner, it was confirmed that the FAU zeolite of the present invention has a higher sphericity and is closer to a sphere than the primary particles of conventional FAU zeolite.

Since the packing density of FAU zeolite is thought to be affected by its _SiO2 / _{Al2O3 molar} ratio, the type of cation, and the water content, the packing densities were compared using zeolites prepared so that these were approximately the same. The FAU zeolite of Example 1, in which the sphericity of the primary particles is 0.60 or more, has a packing density 10% or more higher than the FAU zeolites of Comparative Examples 1 and 2, in which the sphericity is less than 0.60. Similarly, when comparing the FAU zeolites of Example 2 and Comparative Example 3, the packing density is 10% or more higher. The same is true for Example 3 and Comparative Example 4.

Claims (1)

A method for producing FAU type zeolite, comprising: a precursor preparation step of preparing an aqueous mixed solution containing a Si source, an Al source, and seed crystals; and a hydrothermal treatment step of hydrothermally treating the aqueous mixed solution to grow FAU type zeolite crystals, the method being characterized in that silica particles having a specific surface area of 100 ^m2 /g or less are used as the Si source of the aqueous mixed solution containing the seed crystals.

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