JPH0339972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for synthesizing zeolite, and in particular provides a method for synthesizing fine and highly pure offretite crystals, which is a type of zeolite, in a short time. Zeolite, which means boiling stone in Greek, is a crystalline aluminosilicate containing zeolite water. Its basic structure is a SiO ₄ tetrahedron formed around silicon with four oxygen atoms placed at the vertices.
This silicon was replaced by aluminum.
The AlO ₄ tetrahedron has an atomic ratio of O/(Al+Si) of 2.
They are arranged in a regular three-dimensional manner while sharing oxygen so that The negative charge of the AlO ₄ tetrahedron is balanced by the inclusion of alkali metal and alkaline earth metal cations. Furthermore, pores of various sizes are formed depending on the arrangement of the tetrahedrons, and water molecules and exchangeable cations usually exist in the pores. When zeolite is dehydrated or the cations in zeolite are exchanged with other appropriate cations, it can be used as a so-called molecular sieve that has the function of trapping specific molecules in the pores, or it can be reacted only within the pores. It is an industrially valuable substance that is used in various fields, such as as a catalyst, an ion exchanger, and a catalyst carrier. Zeolites are known to have various crystal structures, and these can be distinguished by powder X-ray diffraction patterns. Zeolites also exist naturally, and now naturally occurring zeolites can also be obtained synthetically. Also, zeolites that do not exist naturally can now be synthesized. OFFRETITE, a type of zeolite, also exists in nature, has a hexagonal crystal structure (lattice constants a: 13.3A, c: 7.59A), and has pores that can adsorb cyclohexane. In addition, offretite uses tetramethylammonium ion (hereinafter TMA) in its synthesis reaction system.
The obtained offretite is also called "TMA offretite" because it can be synthesized in the presence of ions (referred to as ions). The chemical composition of this substance is
It _is represented _{by M2O.Al2O3} .( _5-10 ) _SiO2.xH2O . (However, M is TMA, Na and K ions.
The coefficient of M ₂ O fluctuates around 1. x is 0-10. ) TMA ions exist as cations in offretite crystals, and the offretite is heated to 500-600℃.
When fired, TMA ions are decomposed and released to become H ions, which remain in the offretite. As shown in Figure 1, TMA offretite can be clearly distinguished from other zeolites from its powder X-ray diffraction pattern. In particular, zeolites whose chemical composition and crystal structure are similar to offretite include erionite, zeolite T, and ZSM-34, but they have 2θ = 9.6 degrees, 16.6 degrees, which is called the "odd line" on the X-ray diffraction diagram.
Offretite has no peaks at 21.4 degrees and 31.9 degrees (measured using the Kα doublet of copper), so it can be clearly distinguished from these. Generally, zeolites are used as molecular sieves, ion exchangers,
When used as a catalyst, raw zeolite powder is often granulated and used. In this case, in order to enhance the functions of zeolite, ie, separation selectivity, adsorption rate, exchange rate, activity, etc., it is essential that the raw powder has a fine particle size. This can be explained by the fact that the increase in the diffusion rate of adsorbed molecules and ions within the zeolite particles contributes to the improvement of the above-mentioned functions of the zeolite. Also, when a certain type of zeolite is mixed with a different zeolite (as an impurity), pores of different sizes coexist within it.
For example, when this is used as a molecular sieve, the separation of target molecules per unit weight of zeolite becomes extremely poor. In addition, when using this as a catalyst, it has shape selectivity because the pores in the zeolite crystal are the reaction sites (molecules larger than the pores cannot enter the pores and therefore do not react; The catalytic property of not producing molecules larger than the pores will be impaired. Therefore, when using zeolite as a molecular sieve or catalyst, a zeolite with high purity and fine particle size that does not contain foreign zeolites is desired, unless a composite effect is expected by mixing. Offretite is no exception to this matter. Methods for synthesizing TMA offretite have been known for a long time. For example, in Japanese Patent Publication No. 49-27280, the reaction mixture was
A method is disclosed in which TMA offretite is obtained by maintaining it for 8 days, but this method requires a long time for crystallization. Also, in U.S. Patent No. 3578398,
The reaction mixture is kept at room temperature for at least 15 hours, especially for ~24 hours.
By holding (aging) for 7 days, fine
A method of making TMA offretite is disclosed. However, although fine crystals can certainly be obtained with this method, it takes a long time for ripening, and it cannot necessarily be said to be an industrial or economical method. In addition, the same publication discloses that crystallization time can be shortened by crystallizing at a relatively high temperature; however, crystallization at a high temperature may cause analcyme, sodalite, etc. This is not necessarily a preferable method because of the possibility of contamination with impurities. The present inventors have discovered the present invention as a result of intensive research to solve the problems of these conventional synthesis methods. The purpose of the present invention is to provide a method for synthesizing TMA offretite that is free from impurities. The present invention will be further explained. In general, when synthesizing zeolites, there are several important factors that influence the properties of the product. Among these, the composition of the reaction mixture, the temperature and time of crystallization are particularly important, but the state in which the reaction mixture is maintained at the crystallization temperature is also an extremely important factor. The inventors have often experienced that, even if the reaction mixture composition is appropriate, a zeolite with the desired properties cannot be obtained if agitation is applied during crystallization. This is because, except for limited types of zeolites such as mordenite, sodalite, and analcyme, zeolites exist as metastable crystalline phases, so even slight environmental changes are thought to affect crystallization. Therefore,
Conventional zeolite synthesis methods do not involve stirring at all.
The so-called stationary method has become mainstream. The present invention is based on knowledge obtained as a result of various studies regarding stirring conditions during crystallization of zeolite. That is, the present inventors used SiO ₂ , Al ₂ O ₃ , Na ₂ O,
A reaction mixture containing K ₂ O, (TMA) ₂ O and H ₂ O is heated and crystallized without going through a special aging process,
When producing TMA offretite, temperature, _H2O /
There is a complicated relationship between the SiO ₂ molar ratio, (TMA) ₂ /SiO ₂ molar ratio, conditions such as stirring intensity during crystallization, and the product, and only under limited conditions can fine and high-purity crystals be produced. We obtained the knowledge that TMA offretite can be obtained.
The limiting conditions are (1) the reaction mixture composition is H ₂ O/
SiO ₂ = 10 to 70, and (TMA) ₂ O/SiO ₂ =
0.008 to 0.04, (2) the crystallization temperature is 130 to 180°C, and (3) stirring is performed at a circumferential speed of 0.3 m/sec or more at that temperature. Only when these (1) to (3) are satisfied can TMA offretite, which is fine and does not contain any impurities, be obtained in a crystallization time of only a few minutes to 20 hours. The reaction mixture necessary to carry out the invention is:
The composition is not particularly limited as long as it can synthesize TMA offretite, but as mentioned above, at least
H ₂ O/SiO ₂ = 10 to 70, and (TMA) ₂ O/SiO ₂
= 0.008 to 0.04, preferably _H2O / _SiO2 = 12 to 50, (TMA) _2O / _SiO2 =
It is 0.01-0.03. When H ₂ O/SiO ₂ is less than 10, the effect of stirring, which will be described later, is almost lost, and when it exceeds 70, impurities are likely to be generated.
(TMA) ₂ O/SiO ₂ less than 0.008 may result in insufficient crystallization of the product or the formation of impurities.
When it exceeds 0.04, the degree of crystallinity decreases. SiO ₂ source, Al ₂ O ₃ source, Na ₂ O source, K ₂ O source used in the present invention,
(TMA) ₂ O sources are not particularly limited, but from an economical point of view, SiO ₂ sources include amorphous solid silica, water glass; Al ₂ O ₃ sources include sodium aluminate, Al
(OH) ₃ ; Na ₂ O source is NaOH; K ₂ O source is KOH;
(TMA) ₂ Preferably, the O source is a hydroxide or a halide. Although the method of mixing each raw material is not particularly limited, it is preferable to mix the SiO ₂ source after all the alkali sources including the Al ₂ O ₃ source are mixed. The mixed reaction mixture is immediately subjected to a crystallization operation without being aged. The term "ripening" as used herein refers to long-term aging of ten or more hours as in conventional methods, and does not include short-term standing times that inevitably occur during the zeolite synthesis process. The crystallization temperature is determined in carrying out the present invention.
It is essential that the temperature is 130-180°C. The temperature is
If it is less than 130°C, it will take a long time to crystallize, and if it exceeds 180°C, not only will impurities be mixed in, but fine crystals will not be obtained. Since the crystallization temperature in the present invention is higher than the boiling point of the reaction mixture, it is necessary to carry out the crystallization in a sealed container, and it can also be carried out under self-contained pressure or under pressure with an inert gas such as nitrogen. In the present invention, stirring during crystallization is particularly important. In other words, when the maximum diameter during rotation of the stirring blade used for stirring is d (m) and the stirring speed is v (rpm), (π) (d) (v) / (60
) It is essential that the circumferential speed (m/sec) defined as 0.3 m/sec or more is required. The above stirring (1) shortens the crystallization time, (2) makes the crystals finer, and (3) suppresses the formation of impurities. It has the following effects. The importance of stirring in the method of the present invention is that it not only assists in heat transfer in the crystal system, but also in nucleation and
This seems to be due to the subtle influence of the stirring operation on crystal growth. In the present invention, the desired degree of stirring is such that the circumferential speed is 0.3 m/sec or more, more preferably 0.4 to 10 m/sec. The peripheral speed is 0.3
If it is less than 10 m/sec, the effect of the present invention cannot be obtained, and if it exceeds 10 m/sec, it is thought that the intermediate product that transforms the reaction mixture into crystals, that is, the precursor, is destroyed at this stage. , crystallization becomes incomplete. The shape and size of the crystallization tank and stirring blade used in the present invention are not particularly limited, but in order to effectively carry out the present invention, the maximum diameter of the stirring blade described above must be 1/4 of the inner diameter of the crystallization tank. The above is desirable.
Further, the crystallization time is one of the effects of the method of the present invention, and a period of only a few minutes to 20 hours after raising the temperature to the crystallization temperature is sufficient. TMA offretite obtained by the method of the present invention is
After cooling, it is post-treated by known methods such as solid-liquid separation, washing, and drying. Also, the offretite temperature is 500~600℃
After firing, or after the firing, it can be used for various purposes after being subjected to appropriate cation exchange. For example, it can be effectively used as a dehydrating agent, an adsorption/separation agent, and a hydrocarbon conversion catalyst. The present invention will be explained below with reference to Examples, but it is not limited only to these Examples. Example 1 Amorphous solid silica (white carbon manufactured by Nippon Silica Kogyo Co., Ltd.), aqueous sodium aluminate solution (Na ₂ O 18.8w%, Al ₂ O ₃ 21.8wt%), solid NaOH,
A reaction mixture represented by the following formula was prepared from solid KOH, tetramethylammonium hydroxide, and pure water. 0.39(TMA) ₂ O・5.75Na ₂ O・1.15K ₂ O・
Al ₂ O ₃・17.6SiO ₂・325H ₂ O The mixing order was as follows: First, NaOH and KOH were dissolved in pure water, then an aqueous solution of sodium aluminate was added, and finally, amorphous solid silica was added while stirring. . 4000 g of the reaction mixture was placed in an autoclave equipped with a stirrer and crystallized at 170°C. The stirring blade was a turbine type whose maximum diameter when rotating was 1/2 of the autoclave's inner diameter. Stirring intensity (peripheral speed) is 1m/
sec, the time from the preparation of the reaction mixture (after the addition of silica) to the time it was charged into the autoclave was about 1 hour. Autoclave heating time (time from starting heating until crystallization temperature reaches 170℃)
It took about 2 hours. After maintaining at 170℃ for 5 minutes,
After cooling, the solid matter was separated, thoroughly washed with water, and then dried at 110°C for 2 hours. The X-ray diffraction pattern of the product is shown in Figure 1, and it was a highly pure TMA offretite with no impurities observed. In addition, most of the crystals were fine particles with a particle size of 1 μ or less. Examples 2 to 5, Comparative Examples 1 to 8 The same procedure as in Example 1 was conducted except that 200 g of the reaction mixture was charged and the crystallization temperature, crystallization time, and stirring speed were changed, and the results are shown in Table 1. Also, comparative example 4
Figure 2 shows the X-ray diffraction pattern of the crystal obtained in . Example 6, Comparative Examples 9-10 The same procedure as in Example 1 was carried out except that the composition of the reaction mixture was changed and 200 g of the reaction mixture was charged. The results are shown in Table 2.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a powder X-ray diffraction pattern of the crystal obtained in Example 1, and FIG. 2 is a powder X-ray diffraction pattern of the crystal obtained in Comparative Example 4. It was measured using a copper Kα doublet.

Claims (1)

[Claims] 1 SiO ₂ , Al ₂ O ₃ , Na ₂ O, K ₂ O, (TMA) ₂ O
(TMA is tetramethylammonium ion),
In the method of synthesizing zeolite by crystallizing a reaction mixture consisting of H ₂ O, the H ₂ O/SiO ₂ molar ratio is
10 to 70, (TMA) ₂ O/SiO ₂ A zeolite characterized by crystallizing at a temperature of 130 to 180° C. while stirring a reaction mixture having a molar ratio of 0.008 to 0.04 at a circumferential speed of 0.3 m/sec or more. synthesis method. 2. The method according to claim 1, wherein the crystallization time is 20 hours or less.