JP2021172529A - Type-a zeolite single crystal, and method of producing the same - Google Patents

Abstract

To provide a type-A zeolite single crystal with a length of one side thereof being 100 μm or longer, and a method of producing the same.SOLUTION: The synthesis of a type-A cubic zeolite single crystal with a length of one side thereof being 100 μm or longer, can be produced by optimizing the composition of a type-A zeolite synthesis solution. A large-sized type-A zeolite single crystal is expected to develop a novel application of a type-A zeolite, such as a sensor and an electronic device.SELECTED DRAWING: Figure 3

Description

The present invention relates to an A-type zeolite single crystal and a method for producing the same.

Zeolites, which are porous crystals, are roughly classified into natural products and synthetic products. Synthetic zeolites are classified into, for example, A-type, X-type, Y-type, and L-type, depending on their composition and structure, and are molecular sieves and gases. It has functions and characteristics closely related to industry, such as adsorption, ion exchange, and solid acid catalyst. Among zeolites for which more than 100 kinds of skeletal structure species are known, type A zeolite is usually synthesized and used as a powder having a crystal size of 10 μm or less. The A-type zeolite forms a covalent skeleton composed of Al, Si, and O, and has a structure in which nano-sized pores are regularly arranged as shown in FIG. In addition, it has ion exchange characteristics and gas adsorption characteristics, and by applying these characteristics, it is used as a gas adsorbent for detergent builders, dehumidifiers, and the like.

Single crystals of A-type zeolite, which have a larger crystal size, are expected to be indispensable for developing new applications such as gas sensors and electronic devices. Since the first single crystal synthesis report by Charnell in 1971 (Non-Patent Document 1), attempts have been made at home and abroad to increase the single crystal size by improving the synthesis method, and as a result, Al source, Si source, and alkali source. In addition, the amount of triethanolamine (N (C ₂ H ₄ OH) ₃ , hereinafter also referred to as "TEA") added to the synthetic solution depends on the obtained crystal size, and the amount of TEA added is increased. It was shown that the crystal size increased (Non-Patent Document 2). However, there is no report other than the report (Non-Patent Document 3) that a larger A-type zeolite single crystal was obtained by synthesis in outer space (micro-gravity environment) to obtain a cubic single crystal having a maximum length of 85 μm. Incidentally, it has been reported that when synthesized on the ground using a synthetic solution having the same composition, the thickness becomes 50 μm.

Excessive addition of TEA facilitates the formation of X-type zeolite, which is a competing crystalline phase, and thus has a drawback of inhibiting the formation of the desired A-type zeolite. This is one of the reasons why single crystals have not been synthesized. In addition, a method of increasing the ratio of Si source and Al source in the synthetic solution (SiO ₂ / Al ₂ O ₃ ratio) and lowering the mixing temperature of Al source and Si source when preparing the synthetic solution has been reported ( Although Non-Patent Document 4), so far, only a single crystal having a side of 35 to 40 μm has been obtained for type A zeolite.

Further, Patent Document 1 describes a method for producing a single crystal of X-type zeolite having a size of 45 to 70 μm, and Patent Documents 2 and 3 describe a zeolite single crystal having a size of 500 μm or more and a method for synthesizing the same. ing. However, Patent Documents 2 and 3 do not disclose the chemical composition, crystal structure, experimental results for identifying the shape (plate-like, needle-like, spherical, etc.) of the synthesized zeolite, and various crystal structures, It is unclear which of the zeolites having a chemical composition specifically obtained a giant single crystal.
Incidentally, when a follow-up test of the examples of Patent Document 2 was attempted, the powder X-ray diffraction pattern of the product was found in Analcime described in Non-Patent Document 5 [Chemical formula: Na ₁₆ Al ₁₆ Si ₃₂ O ₉₆ · ( H ₂ O) ₁₆ , crystal structure information: space group Ia-3d, lattice constant a = 1.373 nm], and it was found that it was not A-type zeolide.

Japanese Patent No. 2642893 Japanese Patent No. 3718534 Japanese Unexamined Patent Publication No. 11-157998

J. Cryst. Growth (1971) Vol.8, p.291-294 Zeolites (1990) Vol.10, p.44-50 J. Cryst. Growth (2000) Vol.220, p.140-149 Microporous Mesoporous Mater. (2006) Vol.90, p.53-61 Collection of simulated XRD powder patterns for promotings (4th revised edition), Elsevier, Amsterdam (2001) pp. 50-51

An object of the present invention is to provide a large-sized A-type zeolite single crystal that can be used not only as a gas adsorbent, an ion exchanger, and a catalyst, but also as a gas sensor, an electronic device, and the like. Another object of the present invention is to provide a method for producing such a large size A-type zeolite single crystal.

Since porous crystalline zeolite is usually synthesized as a powder in which crystals of about several μm are gathered, its use is mainly for the chemical industry such as ion exchangers, gas adsorbents, and catalysts. The synthesis of zeolite single crystals is known for a plurality of crystal structures and compositions other than type A, and large single crystal substances are the basis for the creation of electronic devices and the like.
Type A is one of the most synthesized and used zeolites, but it is extremely difficult to synthesize large-sized single crystals. In order to use A-type zeolite not only in conventional applications but also in new applications such as electronic devices, a method for synthesizing a larger zeolite under the gravitational environment on the ground and a single crystal obtained from the method are very important.

The present inventor has conducted diligent research on the ratio of constituent raw materials at the time of preparing a synthetic solution by searching for optimized synthetic conditions that are not bound by the previously reported synthetic conditions. As a result, a suitable synthetic condition for increasing the maximum crystal size and making the powder crystal phase obtained from the synthetic solution a single phase was found, and a cube-shaped A-type zeolite single crystal having a side of about 100 μm was obtained on the ground. Succeeded in synthesizing in a gravitational environment.

The points of suitable synthetic conditions are (1) not to excessively increase the amount of triethanolamine added. (2) Do not increase the ratio of Si source and Al source (SiO ₂ / Al ₂ O _{3 ratio) in the synthetic solution.} (3) Do not increase the alkali source (NaOH) for dissolving the Si source and Al source in water. These are the three points (1) to (3), and it is found that the direction is opposite to the conventional synthesis condition, and the optimum synthesis condition can be set by combining these.

The present invention relates to the following (1) to (3) A-type zeolite single crystal or the following (4) A-type zeolite single-phase powder aggregate.
(1) A-type zeolite single crystal having a side length of 100 μm or more.
(2) The A-type zeolite single crystal according to (1) above, wherein the single crystal has a cubic shape.
(3) The A-type zeolite single crystal according to (1) or (2) above, wherein the length of one side of the single crystal is 100 μm to 150 μm.
(4) A powder aggregate of A-type zeolite single phase containing the A-type zeolite single crystal according to any one of (1) to (3) above.

The present invention also relates to the following methods (5) to (8) for producing a type A zeolite single crystal.
(5) The method for producing a type A zeolite single crystal according to any one of (1) to (3) above, wherein each sodium hydroxide aqueous solution of Ai source and Si source and triethanolamine (TEA) are mixed. In terms of the molar ratio _{expressed in terms of oxide, SiO 2} / Al ₂ O ₃ is contained in a ratio of 0.4 to 0.7 and Na ₂ O / Al ₂ O ₃ is contained in a ratio of 1.3 to 1.6. A method for producing a type A zeolite single crystal, wherein a synthetic solution is prepared and the synthetic solution is heated to synthesize a single crystal.
(6) The A according to (5) above, wherein the synthetic solution contains an Ai source represented by an oxide and TEA in a molar ratio of TEA / Al ₂ O ₃ in a ratio of 3.5 to 5.5. A method for producing a type zeolite single crystal.
(7) The method for producing a type A zeolite single crystal according to (5) or (6) above, wherein the synthetic solution is heated at a temperature of 70 to 100 ° C. for 2 weeks or more.
(8) The powder aggregate of the A-type zeolite single phase according to (4) above, which was synthesized from the synthetic solution, was collected by filtration, and the single crystal A-type zeolite single having a side length of 100 μm or more was collected from the powder aggregate. The method for producing a type A zeolite single crystal according to any one of (5) to (7) above, which comprises a step of separating crystals.

According to the present invention, as a single crystal of A-type zeolite, a single crystal having a large size with a side length of 100 μm or more could be obtained. Moreover, such a large single crystal can be obtained by devising synthetic conditions without requiring a special device or a special environment such as weightlessness.
A single crystal of A-type zeolite having a side length of 100 μm opens up new applications for A-type zeolite such as sensors and electronic devices.

Schematic diagram of the crystal structure of A-type zeolite. X-ray diffraction (XRD) data of the A-type zeolite powder synthesized in Examples 1 and 2. Scanning electron microscope (SEM) photograph of the A-type zeolite powder synthesized in Example 1. Scanning electron microscope (SEM) photograph of the A-type zeolite powder synthesized in Example 2. X-ray diffraction (XRD) data of the A-type zeolite powder synthesized in Comparative Examples 1 and 2. A scanning electron microscope (SEM) photograph of the A-type zeolite powder synthesized in Comparative Example 1. Scanning electron microscope (SEM) photograph of the A-type zeolite powder synthesized in Comparative Example 2.

The present invention relates to a large-sized A-type zeolite single crystal having a side length of 100 μm or more and a method for producing the same.

The crystal structure of the A-type zeolite is shown in FIG. A zeolite, unit cell is a = 2.46nm [space group: Fm-3c] a crystal of cubic a general chemical formula of this case is the _{Na 96 Al 96 Si 96 O 384} · 216H 2 O be. The skeleton is composed of Al, Si, and O atoms, and the O atom that connects the Si and Al atoms represented by the lattice points by a covalent bond exists near the center of the ridgeline, but it is omitted in FIG. 1 to make the skeleton structure easier to see. There is. In addition, the same number of commutative Na ⁺ ions as Al are present in the gaps of this skeleton, but these are also omitted. In addition, adsorbed water molecules may also be present in the pores.

The present inventor has succeeded in synthesizing a large size A-type zeolite single crystal of 100 μm or more for the first time by optimizing the synthesis conditions of the A-type zeolite crystal. The points of suitable synthesis conditions are (1) do not excessively increase the amount of triethanolamine (TEA) added, and (2) the ratio of Si source and Al source in the synthesis solution (SiO ₂ / Al ₂ O ₃ ratio). (3) The Si source and the Alkaline source (NaOH) for dissolving the Al source in water are not increased. By combining these points, the synthesis conditions can be optimized.

In the present invention, Al source as can be a metal Al and sodium aluminate and aluminum isopropoxide _{(C 9 H 21 O 3 Al} ) or the like, a high-purity Al metal 99.99 percent aqueous sodium hydroxide It is preferable to dissolve and use it. It is preferable to add all the TEA to the aqueous sodium hydroxide solution containing this Al source.
Further, metal Si, tetraethoxysilane (TEOS), sodium metasilicate, colloidal silica and the like can be used as the Si source, and TEOS having a high purity of 99.99% or more is dissolved in an aqueous sodium hydroxide solution before use. preferable. If a Si source containing more than 0.1% of impurities is used, the number of nuclei generated increases, and as a result, the precipitation of fine crystals increases, so that it is difficult to obtain a large single crystal.

Impurities are removed by passing the above Al source and Si source through a membrane filter of about 0.2 μm, respectively, and then mixed at room temperature. Both the aqueous solution containing the Al source and the Si source are transparent, but the synthetic solution prepared by mixing becomes a uniform milky white color immediately after mixing. In the preparation of this synthetic solution, in order to limit the number of nuclei generated in the early stage of crystallization, it is desirable to mix each solution at room temperature and shorten the mixing time as much as possible. The preparation should be completed.
Further, it is preferable to use all the containers and instruments made of polymer resin for preparing the synthetic solution and performing the reaction. Glass appliances and the like are dissolved in a basic environment, which contributes to contamination with impurities.

_{In the production method of the present invention, SiO 2} / Al ₂ O ₃ is 0.4 to 0.7 and Na in the molar ratio when each of the sodium hydroxide solutions of the Al source and the Si source is expressed as an oxide. Prepare the synthetic solution so that the ratio of ₂ O / Al ₂ O _{3 is 1.3 to 1.6.}
Further, the amount of TEA added to the sodium hydroxide aqueous solution of the Al source is the amount of TEA when added to the sodium hydroxide aqueous solution of the Si source, and the Al source expressed in oxide and TEA are in molar ratio. It is preferable to add TEA / Al ₂ O ₃ in a ratio of 3.5 to 5.5.
When the molar ratio is out of the above range, the X-type zeolite is likely to be mixed as a by-product and consumes the Si source and the Al source. Therefore, it is difficult to obtain a large, high-purity A-type zeolite single crystal.

Next, the synthetic solution thus prepared is crystallized by heating at a temperature of 70 to 100 ° C. for 2 weeks or more to obtain a highly pure A-type zeolite single crystal having a large crystallite diameter. It is known that if the temperature is lower than 70 ° C., it takes too much time to grow a large single crystal, and if the temperature exceeds 100 ° C., polycrystallization occurs or a product having a different crystal structure can be obtained. In order to obtain a large single crystal of 100 μm or more, a reaction time of 1 to 2 months is generally required.

In the crystallization step by heating, the synthetic solution separates into milky white (lower layer) and transparent (upper layer) after heating, but as the crystal growth (synthesis reaction) progresses in the aqueous solution, the interface between the upper layer and the lower layer descends. To go. When the descent of the interface is completely stopped, it is judged that the crystal growth is completed, and the heating is stopped. After that, the product is taken out from the container, washed with ultrapure water and dried to filter and recover the powder aggregate of the A-type zeolite single phase containing the A-type single crystal. A type A zeolite single crystal having a side length of 100 μm or more of the single crystal is separated and recovered from this rough and grainy powder aggregate.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to these examples.
[Synthesis of A-type zeolite single crystal]
In Examples 1 and 2 and Comparative Examples 1 and 2, synthetic solutions having the following compositions were prepared to prepare single crystals of type A zeolite. In Examples 1 and 2 and Comparative Examples 1 and 2, the synthesis conditions other than the composition of the synthesis solution are as described in 1) to 5) below, and are the same.

The chemical composition of each synthetic solution when other than TEA is expressed as an oxide is as follows.
(Example 1)
Al ₂ O ₃ : SiO ₂ : Na ₂ O: TEA: H ₂ O = 1: 0.55: 1.42: 4.5: 200
(Example 2)
Al ₂ O ₃ : SiO ₂ : Na ₂ O: TEA: H ₂ O = 1: 0.55: 1.42: 4.5: 200
(Comparative Example 1)
Al ₂ O ₃ : SiO ₂ : Na ₂ O: TEA: H ₂ O = 1: 1.12: 2.02: 5.8: 200
(Comparative Example 2)
Al ₂ O ₃ : SiO ₂ : Na ₂ O: TEA: H ₂ O = 1: 0.70: 1.72: 8.0: 200

1) As an Al source, an Al metal having a purity of 99.99% (4N) or more is dissolved in an aqueous sodium hydroxide solution, and TEA is added.
2) As a Si source, TEOS having a purity of 99.9999% (6N) or more is dissolved in an aqueous sodium hydroxide solution, and TEA is added as necessary.
3) Both the Al source and the Si source are passed through an Advandec 0.2 μm membrane filter to remove impurities, and then mixed at room temperature. Both the Al source and the Si source are transparent, but the synthetic solution after mixing becomes a uniform milky white color immediately after mixing.

4) Enclose the synthetic solution in a transparent container whose contents can be confirmed, and heat to 80 ° C.
5) The aqueous solution separates into a milky white lower layer and a transparent upper layer, but as the synthetic reaction proceeds in the aqueous solution, the interface between the upper layer and the lower layer descends. When the descent of the interface is completely stopped, it is judged that the crystal growth is completed, and the heating is stopped. The product is taken out of the container, washed with ultrapure water, and then dried to recover a grainy A-type zeolite single-phase powder aggregate containing A-type single crystals. It takes 1 to 6 months to complete the synthetic reaction.

The crystal outline and size of the obtained product were evaluated by scanning electron microscope (SEM) observation, and the crystal phase of the product was identified by powder X-ray diffraction. Hitachi S4800 (acceleration voltage 2KV) was used as the SEM. For powder X-ray diffraction (XRD), a diffraction pattern of 2θ = 5 to 50 ° was obtained from the _{Cu-Kα 1,2 characteristic line using Rigaku SmartLab.}

[Results of Examples 1 and 2]
The XRD pattern of the A-type zeolite powder synthesized in Example 1 (Sample 1) and Example 2 (Sample 2) is shown in FIG. When 2θ≤9 °, the diffraction line intensities are set to 1/2 and 1/10, respectively. Since all the diffraction line peaks observed in the XRD data of Sample 1 belong to the A-type zeolite, it is a single-phase A-type zeolite. On the other hand, sample 2 has some impurities indicated by "↓", but the other diffraction line peaks are attributed to the A-type zeolite.

The results of observing the products of Examples 1 and 2 by SEM are shown in FIGS. 3 and 4, respectively.
As shown in FIG. 3, the A-type zeolite crystal, which is the product of Example 1, has a cube-based shape, and the length of one side (ridge) thereof reaches a maximum of about 90 μm. Moreover, the crystal surface is smooth. On the other hand, in the product obtained in Example 2 shown in FIG. 4, a cube-shaped A-type zeolite crystal was observed as the main phase as in FIG. 3, and the length of one side of the cube crystal was up to about 100 μm. Reach. However, although amorphous particles of less than 10 μm are present on the surface of a single crystal or the like, these are considered to correspond to the impurities observed in the XRD data of FIG. This impurity can be removed by dispersing the product in water and removing the supernatant liquid after ultrasonic treatment.

[Results of Comparative Examples 1 and 2]
The XRD pattern of the product in Comparative Examples 1 and 2 is shown in FIG. When 2θ≤9 °, the diffraction line intensity is multiplied by 1/4 in both Comparative Examples 1 and 2.
In Examples 1 and 2, the A-type zeolite was a single-phase or main component, whereas in Comparative Examples 1 and 2, the amounts of TEA, Si source, and sodium hydroxide were increased according to the conventional synthesis guideline or reported example. The crystal size was increased by synthesizing in many environments. As a result, not only the diffraction line peak derived from the X-type zeolite is observed in the XRD pattern, but also the X-type zeolite is rather the main component in Comparative Example 2.

6 and 7 are SEM images of the products of Comparative Examples 1 and 2, respectively. A crystal having a hexahedral cube shape (one side shape is a square) is a type A zeolite, whereas a crystal having a regular octahedron shape (one side shape is a regular triangle shape) is a single crystal. Or, it was confirmed that it was present on the surface of the cube shape. In Comparative Example 1, the A-type zeolite crystal had a maximum side of 50 μm, and the X-type zeolite crystal had a maximum side of 20 μm. On the other hand, in Comparative Example 2, the A-type zeolite crystal had a maximum side of about 35 μm, and the X-type zeolite crystal had a maximum side of about 76 μm on the regular triangular surface. As described above, A-type zeolite crystals having a size larger than those of Examples 1 and 2 could not be realized in Comparative Examples 1 and 2.

Claims (8)

A type zeolite single crystal having a side length of 100 μm or more. The A-type zeolite single crystal according to claim 1, wherein the single crystal has a cubic shape. The A-type zeolite single crystal according to claim 1 or 2, wherein the length of one side of the single crystal is 100 μm to 150 μm. A powder aggregate of A-type zeolite single phase containing the A-type zeolite single crystal according to any one of claims 1 to 3. The method for producing a type A zeolite single crystal according to any one of claims 1 to 3, wherein each sodium hydroxide aqueous solution of an Al source and a Si source and triethanolamine (TEA) are mixed and represented by an oxide. _{A synthetic solution containing SiO 2} / Al ₂ O ₃ in a ratio of 0.4 to 0.7 and Na ₂ O / Al ₂ O ₃ in a ratio of 1.3 to 1.6 was prepared. , A method for producing a type A zeolite single crystal, wherein the synthetic solution is heated to synthesize a single crystal. The A-type zeolite single crystal according to claim 5, wherein the synthetic solution contains an Al source represented by an oxide and TEA in a molar ratio of TEA / Al ₂ O _{3 in a ratio of 3.5 to 5.5.} Manufacturing method. The method for producing a type A zeolite single crystal according to claim 5 or 6, wherein the synthetic solution is heated at a temperature of 70 to 100 ° C. for 2 weeks or more. The powder aggregate of the A-type zeolite single phase according to claim 4 is filtered and recovered from the synthetic solution, and the A-type zeolite single crystal having a side length of 100 μm or more of the single crystal is separated from the powder aggregate. The method for producing a type A zeolite single crystal according to any one of claims 5 to 7, which comprises a step.

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