JP2013049602A - Method of manufacturing fine zeolite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing fine zeolite with no amorphous substance or a very little amount of amorphous substance because when fine zeolite crystal with a particle size of ≤0.5 μm or less is manufactured by crushing zeolite, the zeolite is made amorphous, crystallinity is degraded, and original performance of the zeolite can not be achieved.SOLUTION: The fine zeolite with the particle size of ≤0.5 μm obtained by crushing zeolite once is dispersed in a silicate solution having a specific composition, and is recrystallized to manufacture the fine zeolite with no amorphous substance or a very little amount of amorphous substance. The obtained zeolite fine particle exhibits improved crystallinity, and achieves excellent performance such as catalyst characteristics.

Description

  The present invention relates to a method for producing fine zeolites, and more particularly to a method for producing fine zeolites having no or very little amorphous.

Zeolite has excellent ion exchange characteristics, adsorption characteristics, and catalytic characteristics, and is widely used in the consumer and industrial fields. In general, the particle size of zeolite used as an ion exchange material, an adsorbent, and a catalyst is 0.5 to several μm, but diffusion in the zeolite pores of the target molecule may be rate-limiting for various reactions. Therefore, in recent years, research on synthesis of zeolite nanoparticles having a particle size of 100 nm or less has been actively conducted to improve diffusion and reaction rate (for example, Non-Patent Document 1, the obtained zeolite is initially about 40-80 nm, When hydrothermal synthesis is continued, grains grow to 200-400 nm.)
Research on conventional zeolite nanoparticle synthesis has been achieved mainly by bottom-up methods, that is, using quaternary ammonium salts and special organic substances to control nucleation and crystal growth. However, since zeolite synthesis uses an extremely inexpensive alkali source such as sodium hydroxide, sodium silicate, sodium aluminate or the like as a raw material, the use of organic substances greatly affects the final cost even in a small amount. Therefore, establishment of a novel nanozeolite manufacturing process that does not use organic substances during synthesis is desired.
As a method for producing such a fine zeolite, grinding of a zeolite having a larger particle diameter has been carried out. (Patent document 1). It is estimated that the amorphous ratio in the zeolite thus pulverized usually reaches 30% or more.
On the other hand, the present inventors have confirmed that the amorphous layer on the zeolite surface is dissolved and removed by the aluminosilicate solution (Non-patent Document 2).
Furthermore, the present inventors have announced that fine zeolite with less amorphousness can be obtained by recrystallizing the pulverized zeolite in an aluminosilicate solution (Non-patent Document 3).

JP 2003-146649 A

Science vol. 283, 958-960 (1999) Microporous and Microporous Material 70, 17-13 (2004) Cryst. Growth & Design 11, 955-958 (2011)

  If an attempt is made to produce fine zeolite crystals having a particle size of 0.5 μm or less by pulverizing the zeolite, it becomes amorphous and the crystallinity is lowered, and the original performance of the zeolite cannot be exhibited. The present invention provides a method for producing fine zeolite crystals with no or very little amorphous.

The present inventors have found that a fine zeolite having a particle size of 0.5 μm or less obtained by pulverization of zeolite or the like is dispersed in a silicate solution having a specific composition and recrystallized, so that there is no amorphous or very It has been found that a very small amount of fine zeolite can be produced, and the present invention has been completed.
That is, the present invention has the following composition formula: aM ¹ ₂ O · bSiO ₂ · Al ₂ O ₃ · cMeO
(In the formula, M ¹ represents an alkali metal, proton, or ammonium ion (NH ₄ ⁺ ), Me represents an alkaline earth metal, and a = 0.01 to 1, b = 20 to 80, c = 0. ~ 1)
Zeolite (starting material) represented by the following composition formula: AM ² ₂ O / BSiO ₂ / CH ₂ O
(Wherein M ² represents an alkali metal, A / C (molar ratio) is 0.003 to 0.010, and B / C is 0.006 to 0.025). Is a process for producing fine zeolite having an average particle size of 0.01 to 0.5 μm.

The SEM photograph of the zeolite after the recrystallization process obtained in Example 1 is shown. The X-ray-diffraction spectrum of the zeolite grind | pulverized in Example 1 and the zeolite after a recrystallization process is shown. The TEM photograph of the zeolite grind | pulverized in Example 1 and the zeolite after a recrystallization process is shown. The shaded portion (shaded portion) indicates a crystal generated by recrystallization.

  The present invention is a process for producing a fine zeolite comprising dispersing a zeolite (starting material) in a silicate solution having a specific composition and recrystallization.

The starting zeolite is represented by the following general formula (composition formula).
^{_{aM 1 2 O · bSiO 2 ·}} Al 2 O 3 · cMeO
Wherein, M 1 ² _O and MeO represents a cation which is present for charge compensation in the zeolite framework.
M ¹ represents an alkali metal, a proton, or an ammonium ion (NH ₄ ⁺ ). As the alkali metal, K or Na is preferable.
Me represents an alkaline earth metal, preferably Mg or Ca.
M ¹ and Me represent cations present in the zeolite skeleton. At the time of producing the zeolite, these cations are preferably alkali metals or alkaline earth metals from the viewpoint of raw materials. When this zeolite is used as a catalyst or the like, the alkali metal or alkaline earth metal is often used after being exchanged for proton (H ⁺ ) or ammonium ion (NH ₄ ⁺ ), preferably proton. However, any of these zeolites can be used as the starting material of the present invention.

a represents 0.01-1.
b represents 20 to 80 (that is, Si / Al = 10 to 40), preferably 30 to 60 (that is, Si / Al = 15 to 30).
For recrystallization of zeolite having a relatively low Si / Al ratio (1-30), it is appropriate to use an aluminosilicate solution (Non-patent Document 3, Japanese Patent Application No. 2010-118304), whereas Si / Al For recrystallization of zeolites with a relatively high ratio (10-40), it may be appropriate to use a silicate solution.
c represents 0-1.
The structure of the zeolite is not particularly limited, and may be any of FAU, CHA, BEA, MFI, MOR, and FER (each zeolite structure defined by the International zeolite association).

This zeolite may be obtained by pulverizing zeolites represented by the same composition formula, or may be obtained by pulverizing a plurality of zeolites represented by different composition formulas. Usually, the size of the zeolite before pulverization (for example, the average particle diameter measured by a laser diffraction method) is 0.15 μm or more, for example, about 0.15 to 15 μm.
This pulverization method may be any method, but can be performed using a ball mill, a bead mill, a planetary ball mill, a jet mill or the like. Among these, the bead mill can minimize the amorphization of the zeolite. The bead mill is a device that normally uses 50 to 500 μm ceramic beads for crushing and crushing. Because fine beads are used for the grinding media, unlike the ball mill and planetary ball mill, the powder to be processed often collides with the beads and other particles, and the force applied to the particles during a single collision is small, so the surface It can be efficiently pulverized without making it amorphous. However, even if a bead mill is used, the zeolite becomes amorphous to some extent.
As a result of this pulverization, the average particle size of the zeolite is set to about 0.01 to 0.5 μm and used in the production method of the present invention.

In the production method of the present invention, this zeolite is dispersed in a silicate solution having the following composition (representing the components in the solution and the mixing ratio thereof).
AM ² ₂ O / BSiO ₂ / CH ₂ O
In the formula, M ² represents an alkali metal, preferably K or Na.
A / C (molar ratio, the same applies hereinafter) is 0.003 to 0.01, and B / C is 0.006 to 0.025. Recrystallization may be difficult under composition conditions outside this range.
This silicate solution can be obtained by dissolving M ² OH (wherein M ² is as described above) and SiO ₂ in water at a mixing ratio that gives the above composition. Since the recrystallization treatment is often close to the synthesis temperature at which the corresponding zeolite is produced, the water temperature is preferably about 100 to 230 ° C.

When the zeolite is dispersed in the silicate solution, the amorphous layer is dissolved in the solution (Non-patent Document 2), and the dissolved zeolite is considered to recrystallize on the remaining zeolite crystals.
The conditions for this silicate solution treatment are as follows:
Temperature: 100-230 ° C
Processing time: 1 to 24 hours, usually about 2 hours.
Container: Although there is no restriction | limiting in particular, Since a water | moisture content boils above 100 degreeC, it is preferable to use a sealed autoclave.
The amount of zeolite in the silicate solution is usually about 0.5 to 10 g with respect to 100 ml of the silicate solution. For example, in the case of MFI type zeolite, about 1 to 3 g is preferable.

  As a result of this treatment, there can be no or very little amorphous parts of the resulting zeolite crystals. The disappearance of this amorphous part and the increment of zeolite crystals due to recrystallization depends on the extent of this treatment. If the treatment is thoroughly performed (for example, the treatment is performed for a long time), the amorphous portion can be substantially eliminated, and the zeolite crystals can be further increased by recrystallization. On the other hand, if it is only necessary to reduce the amorphous portion to some extent, this process may be stopped halfway (for example, the process is stopped in a short time).

The generated zeolite is represented by the following general formula (composition formula) as in the case of the starting material.
aM ³ represented by _{2 O · bSiO 2 · Al 2} O 3 · cMeO.
a to c are defined as in the starting material. As explained below, it is not exactly the same as the starting material. M ³ is a mixture of M ¹ and M ² . In addition, since Me contained in the zeolite is used as it is or is released into the solution, and a part or all of it is recrystallized, c is equal to or less than c of the starting material.

When recrystallization is performed using zeolite as a nucleus in a solution in which Al and Si are mixed, it is considered that recrystallization is performed while incorporating Si so that the Al in the solution has the same structure as the zeolite crystal of the nucleus.
When a silicate solution is used as a solution for recrystallization as in the present invention, all of the Al present in the solution is a solution of the amorphous part of the zeolite, and the dissolved amorphous part Is considered to recrystallize as it is. As a result, the composition of the recrystallized crystal is very close to the composition of the core crystal, and as a result, the composition (Si / Al ratio, etc.) becomes uniform. Further, if Al is not present at all, the crystallization does not proceed and only Si is taken into the zeolite and no grain growth occurs. For this reason, it is considered that if the Al present in the solution disappears, the progress of crystallization stops, and as a result, the crystallization can be enhanced while being fine.
On the other hand, when an aluminosilicate solution is used as a solution for recrystallization, there is more Al in the solution than that in which the amorphous part of the zeolite is dissolved. Since the crystallization takes place, the composition tends to be Al richer than the composition of the core crystals compared to the case where the silicate solution is used, and as a result, the composition such as the Si / Al ratio becomes non-uniform. (See Table 1 below). Moreover, since it grows taking in both Si and Al in a solution, it is thought that there exists a tendency for a size to become larger.

If the Si / Al ratio of the zeolite after treatment is too low, the amount of Al, which is an acid point, increases and the desired catalytic reaction does not proceed due to coking. If it is too high, a layered compound precipitates as a by-product. Therefore, it is preferable to be within about -15 to + 50% compared to before treatment. In addition, since the crystallinity of the zeolite after the treatment is proportional to the existence ratio of the crystals, it is desirable that it is 90% or more as compared with that before the treatment.
Further, the average particle size of the zeolite obtained as a result of the above treatment is almost the same as the average particle size before the treatment.

The following examples illustrate the invention but are not intended to limit the invention.
The X-ray photograph is a scanning electron microscope (SEM) (S5200, manufactured by Hitachi, Ltd.), the X-ray diffraction (XRD) is an automatic X-ray diffractometer (RINT2500, manufactured by Rigaku Corporation), and the inductively coupled plasma analysis is Measurement was performed using an IPC emission spectrometer (ICPE-9000, manufactured by Shimadzu Corporation). The average particle diameter of the zeolite was measured by a laser diffraction method using a laser diffraction particle size distribution analyzer (SALD-7000, manufactured by Shimadzu Corporation) after dispersing the zeolite in water (concentration 0.01 wt% or less).

Example 1
Add 1.2 g of dispersant (Cerna E503, manufactured by Chukyo Yushi Co., Ltd.) to 100 ml of ethanol, and add 60 g of MFI-type zeolite (NH ₄ Si ₁₉ AlO ₄₀ , 840NHA manufactured by Tosoh Corporation, average particle size 2.5 μm) to slurry. Adjusted. Meanwhile, a bead mill (MiniCer manufactured by Ashizawa Finetech Co., Ltd.) using ZrO ₂ beads having a diameter of 300 μm was filled with ethanol, the rotating shaft was rotated at 3000 rpm, and 432 g of the slurry was charged over 8 minutes. After the addition, the slurry pulverized for 30 to 480 minutes was collected and dried on a magnetic dish at 150 ° C. for 3 hours to collect the powder.
An SEM photograph of the raw material and the obtained pulverized zeolite is shown in FIG. The raw material zeolite was pulverized to an average particle size of 200 nm or less after pulverization for 120 minutes, and pulverized to an average particle size of 50 nm after 480 minutes (FIG. 1 left).
Moreover, the X-ray-diffraction spectrum of a raw material and the obtained ground zeolite is shown in FIG. After 480 minutes of pulverization, the peak intensity derived from the MFI crystal (plural diffraction peaks observed at 2θ = 22 to 25 degrees) is decreased. From the peak area ratio of the X-ray diffraction spectrum, the amorphous ratio in the zeolite is estimated to be about 90 wt%. This shows that the amorphization of the zeolite particles is progressing with the progress of the grinding time.

Next, NaOH and SiO ₂ (both manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in water to prepare six types of silicate solutions having the following compositions.
0.292Na ₂ O: xSiO ₂ : 55.5H ₂ O (S1: x = 0.400, S2: x = 0.650, S3: x = 0.800, S4: x = 1.00)
yNa ₂ O: 0.650SiO ₂ : 55.5H ₂ O (S5: y = 0.165, S6: y = 0.55)
The pulverized sample obtained above was treated in this silicate solution at 180 ° C. for 2 to 24 hours (hereinafter referred to as “S treatment”). The solution containing the sample was centrifuged at 3500 rpm for 30 minutes using a centrifuge to separate the precipitate (zeolite) from the solution. The precipitate (zeolite) was collected, dispersed in ion-exchanged water, and the sample was sufficiently washed by repeating the same centrifugation. The washed product was dried at 300 ° C. for 4 hours to make it anhydrous.

An SEM photograph of a zeolite (hereinafter referred to as “S2 zeolite”) obtained using a silicate solution having the composition of S2 is shown in FIG. From this photograph, it can be seen that the particle size is about 30 to 300 nm and the average is 60 nm (right in FIG. 1).
Further, an X-ray diffraction spectrum of the S2 zeolite fine particles is shown in FIG. The peak intensity (total of diffraction peak areas at 2θ = 22 to 25 degrees) is increased, indicating that recrystallization has progressed. In addition, the ratio of amorphous content in the zeolite is estimated to be 2 wt% from the peak area ratio of X-ray diffraction spectrum of S2 zeolite fine particles (total of diffraction peak areas of 2θ = 22 to 25 degrees). You can see that the quality is decreasing.
A TEM photograph of S2 zeolite is shown in FIG. It can be seen that fine particles with high crystallinity without or very little amorphous layer are obtained after recrystallization.
Further, the BET surface area (total surface area in the pores and the surface area of the particles) of the obtained raw material, 480-minute pulverized sample, and S2 zeolite was measured by nitrogen adsorption measurement to be 443 m ² g ⁻¹ and 223 m ² g ^{−, respectively. 1} , 497 m ² g ⁻¹ . Although the surface area is increased by pulverization after the pulverization, the BET surface area is considered to have decreased from 443 m ² g ⁻¹ to 223 m ² g ⁻¹ because the pores became amorphous by pulverization. On the other hand, after recrystallization, the amorphous zeolite changed to crystals, and the BET surface area is thought to have increased from 223 m ² g ⁻¹ to 497 m ² g ⁻¹ .

Comparative Example 1
Al (OH) ₃ , NaOH and SiO ₂ (all manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in water to prepare an aluminosilicate solution having the following composition.
0.292Na ₂ O :: 0.650SiO ₂ : zAl (OH) ₃ : 55.5H ₂ O (AS1: z = 0.05, AS2: z = 0.10)
Next, the pulverized zeolite obtained in the same manner as in Example 1 was treated in this aluminosilicate solution at 180 ° C. for 2 to 24 hours (hereinafter referred to as “AS treatment”). Zeolite fine particles were obtained.

The relative crystallinity of the zeolite fine particles obtained in Example 1 and Comparative Example 1 relative to the Si / Al ratio, the recovery rate, and the raw material calculated from X-ray diffraction as 100% is shown in the table below. The recovery rate was obtained by comparing and calculating the dry weight of the zeolite before and after the S treatment or AS treatment. The Si / Al ratio was determined with an ICP emission spectrometer.

  The Si / Al ratio of the zeolite obtained in Example 1 is closer to that of the raw material zeolite than the Si / Al ratio of the zeolite obtained in Comparative Example 1 over almost all the treatment time. This indicates that the zeolite crystal formed by recrystallization has the same or close crystal structure as the zeolite crystal before pulverization. On the other hand, zeolite recrystallized using an aluminosilicate solution contains zeolite having a Si / Al ratio different from that of the zeolite crystals before pulverization, and is considered to be a zeolite having a non-uniform crystal structure.

Example 2
In the zeolite (S2) obtained in Example 1, Na ions are present in the zeolite pores after the S treatment. In order to evaluate the acid catalytic ability, all the cations present in the pores were ion exchanged with H ⁺ . Specifically, 1 g of zeolite was stirred in a 1 mol / l ammonium nitrate solution (Wako Pure Chemical Industries, Ltd.) at room temperature for 1 hour, and the zeolite was recovered by centrifugation. This operation was performed three times. After this stirring operation, all the cations in the zeolite pores became NH ₄ ^+, and this was calcined at 400 ° C. for 1 hour to obtain a zeolite containing only H ⁺ cations by the following reaction.
NH ₄ ⁺ → NH ₃ + H ⁺

10 mg of this zeolite (catalyst) was placed in a reaction tube and allowed to stand at 400 ° C. for 1 hour under a flow of helium at a flow rate of 25 ccmin ⁻¹ . After that, the temperature of the catalyst is lowered to 300 ° C., and then 1.0 μl of cumene (manufactured by Wako Pure Chemical Industries, Ltd.) is injected under the same helium flow conditions, and the zeolite is cracked into benzene and propylene by the following formula (zeolite). The catalytic properties of were evaluated.
The obtained benzene was traced using a TCD gas chromatograph (GC-6A manufactured by Shimadzu Corporation), and the conversion rate of cumene was calculated from the peak area of the obtained benzene. This operation was performed 10 times, and the cumene conversion rate during the 10th reaction was compared.
As a result, the cumene conversion rate was 95.6%.
For comparison, the same reaction was performed using the raw material zeolite used in Example 1 and the zeolite obtained by pulverizing this in 480 minutes in Example 1 instead of the above zeolite. The conversion rate of cumene was 70.2% when the raw material zeolite was used, and 68.8% when the zeolite pulverized for 480 minutes was used.

Comparative Example 2
The same reaction as in Example 2 was performed using the zeolite obtained in Comparative Example 1. Cumene conversion was 83%. It can be seen that an excellent catalyst having a high conversion rate of Example 1 obtained by recrystallization using a silicate solution was obtained.
The reason for such a difference is presumed as follows: That is, the composition such as the Si / Al ratio of the zeolite recrystallized in the silicate solution of the present invention as described above has little variation, Close to the composition of the zeolite (Table 1). This is considered that the crystal structure of the recrystallized zeolite is more uniform. On the other hand, the composition of the zeolite obtained by using the aluminosilicate solution as the solution for recrystallization is more heterogeneous, and although it has the same crystal structure as a whole, the surface layer is considered to be a zeolite containing more Al. . Since the catalytic activity of zeolite is largely dependent on the crystal structure and composition of the zeolite, it is considered that the zeolite according to the present invention has a higher homogeneous and fine zeolite.

Claims (2)

The following composition formula: aM ¹ ₂ O · bSiO ₂ · Al ₂ O ₃ · cMeO
(In the formula, M ¹ represents an alkali metal, proton, or ammonium ion (NH ₄ ⁺ ), Me represents an alkaline earth metal, and a = 0.01 to 1, b = 20 to 80, c = 0. ~ 1)
Zeolite (starting material) represented by the following composition formula: AM ² ₂ O / BSiO ₂ / CH ₂ O
(Wherein M ² represents an alkali metal, A / C (molar ratio) is 0.003 to 0.010, and B / C is 0.006 to 0.025). A method for producing a fine zeolite having an average particle size of 0.01 to 0.5 μm, comprising dispersing in a glass and recrystallization. The process according to claim 1, wherein the zeolite (starting material) is obtained by pulverizing a zeolite having an average particle size of 0.15 µm or more and represented by the above composition formula.