JPH1053410A - Production of low-silica x-type zeolite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject zeolite excellent in absorptive performance with a specified silica/alumina molar ratio by aging a mixed gel shown by a specific compositional formula at a specified temperature followed by crystallization. SOLUTION: First, NaOH is added to an aqueous sodium aluminate solution to form a solution A which is then cooled to about <=30 deg.C; while an aqueous sodium silicate solution B is left to cool to about <=30 deg.C. Secondly, the aqueous solution B is added to the aqueous solution A under agitation to effect completion of gelatin while the whole system is kept at about <=30 deg.C, thus forming a mixed gel with the composition formula: 2.4-237Na2 O.Al2 O3 .2.7-2.8SiO2 .120-140 H2 O. Thirdly, the mixed gel is aged at <=35 deg.C for about 24h and then heated to about 85-95 deg.C and kept at that temperature for input 15h or longer to effect completion of the crystallization. Subsequently, the crystallized product is put to filtration, washed with water or warm water, and then dried at about 90-100 deg.C, thus obtaining the objective low-silica X-type zeolite with the silica/ alumina molar ratio of 2.20-2.40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an X-type zeolite having a low silica / alumina molar ratio. More specifically, silica / alumina having an extremely high adsorption capacity and suitable for use in, for example, separating and concentrating oxygen from a mixed gas containing nitrogen and oxygen as main components by an adsorption separation method, and the like. Molar ratio of 2.20 to
The present invention relates to a method for producing an X-type zeolite of 2.40.

[0002]

2. Description of the Related Art Usually, the molar ratio of silica / alumina in a synthesized X-type zeolite is 2.5,
It is known that the coexistence of KOH in addition to OH reduces the silica / alumina molar ratio to 2.0. Reducing the silica / alumina molar ratio of the zeolite increases the number of aluminum atoms in the crystal and therefore the number of cations. In general, adsorption of molecules such as nitrogen and oxygen on zeolite is called physical adsorption, and the larger the number of cations, the larger the adsorption capacity.

Various methods have been proposed for producing low silica X-type zeolites. For example, JP
Japanese Patent Publication No. -8400 and Japanese Patent Publication No. 5-25527 describe a method for producing a low silica X-type zeolite having a silica / alumina molar ratio of 2.0, but according to these methods, a potassium salt is added. Is essential, and the temperature conditions for gelation are low, and the synthesis is not easy.

Japanese Patent Application Laid-Open No. Sho 61-222919 discloses a method for producing a low silica X-type zeolite compact by converting a compact from kaolin-type clay into metakaolin and then crystallization. Have been described. According to the method, in order to obtain a high-purity low-silica X-type zeolite molded body, a large amount of a pore-forming substance (organic substance) is added during the production of a kaolin molded body, heated and burned to produce porous metakaolin. It is necessary to form a compact and then crystallize it. However, in this method, extremely large heat is generated due to the combustion of the organic matter, so that the temperature control is difficult,
It is extremely difficult to properly control the pores of the molded product, and it is therefore difficult to obtain a high-purity low-silica X-type zeolite molded product.

[0005]

SUMMARY OF THE INVENTION In order to avoid the above-mentioned difficulties, the present invention does not require the addition of a potassium salt.
An object of the present invention is to provide a method for producing a low-silica X-type zeolite having a silica / alumina molar ratio of 2.20 to 2.40 in a temperature range for synthesizing a normal X-type zeolite.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on each factor in the production of low-silica X-type zeolite, and studied the charge composition of sodium aluminate and sodium silicate as raw materials and the gel during the production process. By appropriately controlling the conditions such as temperature and time in crystallization and crystallization, a low silica X-type zeolite having a silica / alumina molar ratio of 2.20 to 2.40 can be produced. The silica / alumina molar ratio is 2.20-2.
The low silica X-type zeolite having a value of 40 has a low silica content as compared with the conventionally produced X-type zeolite, that is, has a high adsorption performance due to a large number of aluminum atoms in the crystal, The inventors have found that the heat resistance is superior to that of the low silica X-type zeolite having a silica / alumina molar ratio of about 2.0, and completed the present invention.

Hereinafter, the present invention will be described in detail. The method for producing a low silica X-type zeolite having a silica / alumina molar ratio of 2.20 to 2.40 according to the present invention is from 2.4 to 2.7.
_{Na 2 O · Al 2 O 3} · 2.7~2.8SiO 2 · 120~
After aging the mixed gel composed of 140H ₂ O at a temperature of 35 ° C. or less, it is crystallized at a temperature of 85 to 95 ° C.

Here, when the silica / alumina molar ratio of the X-type zeolite is less than 2.20, its heat resistance deteriorates, and when it exceeds 2.40, the silica content is large, that is, the aluminum atom in the crystal Is not preferred because the adsorption performance is lowered due to the decrease in the number.

The production method includes the steps of preparing a raw material into a solution and cooling, mixing the raw material solution to form a gel, aging, aging the heated gel to crystallize it, washing and drying. Step, a step of shaping the product as necessary, a step of ion exchange with calcium ions and the like as needed, a step of activating,
A low-silica X-type zeolite having a silica / alumina molar ratio of 2.20 to 2.40 can be easily produced.

Hereinafter, each step will be described.

<Preparation of Raw Materials> A starting material, sodium aluminate, is diluted with water to form an aqueous solution, and a solution obtained by adding sodium hydroxide to the aqueous solution (hereinafter, referred to as solution A) is cooled. Here, sodium aluminate may be a solid or a solution previously diluted with water. Regarding the cooling, it is desirable that the temperature of the solution A be 30 ° C. or lower in order to generate the desired low silica X-type zeolite in the following steps. The cooling method is not particularly limited as long as the temperature of the solution A can be controlled to 30 ° C. or lower. For example, the purpose can be achieved by cooling. Next, a solution obtained by diluting sodium silicate (No. 3 Keiso) with water (hereinafter referred to as solution B) is allowed to cool to 30 ° C. or lower as in the case of solution A. In the aqueous sodium aluminate solution and the aqueous sodium silicate solution described above, any concentration can be applied as a diluted aqueous solution as long as the object of the present invention can be achieved.

Here, the composition of the charged raw materials is 2.4 to
_{2.7Na 2 O · Al 2 O 3} · 2.7~2.8SiO 2 · 1
20 to 140 H ₂ O, and the respective molar ratio to Al ₂ O ₃ is silica / alumina molar ratio 2.20 to 140
It is an important factor in producing low silica X-type zeolite of 2.40.

The reason is that if the molar ratio of Na ₂ O / Al ₂ O ₃ is lower than 2.4, the formation of X-type zeolite having a silica / alumina molar ratio of 2.5 or the gel may be present as it is. Silica / Higher than 2.7
X-type zeolite or P having an alumina molar ratio of 2.5
It is often found that impurities such as type zeolite coexist, which is not preferable. When the molar ratio of SiO ₂ / Al ₂ O ₃ is lower than 2.7, the zeolite is A-type zeolite. When the molar ratio is higher than 2.8, the zeolite having a silica / alumina molar ratio of 2.5 or higher. Jasite-type zeolite is undesirably formed. Further, when the molar ratio of H ₂ O / Al ₂ O ₃ is lower than 120, the slurry concentration becomes high, the heat conduction is poor, and the slurry tends to be non-uniform, so that the number of small crystal nuclei increases and the generated crystals are small. Further, X-type zeolite or P-type zeolite having a silica / alumina molar ratio of 2.5 as an impurity easily coexists. On the other hand, when the ratio is higher than 140, the slurry concentration is low and large crystals are easily obtained, but the crystallization time is undesirably long.

<Gelling> Next, Solution B is added while stirring Solution A, and stirring is continued until no lumps are formed.
Complete gelation while maintaining below 0 ° C. Where A
As for the mixing of the solution and the solution B, it is preferable to mix the two solutions at a time in order to promote the gelation uniformly, and there is no particular limitation on the mixing order of the solution A and the solution B. As the time for gelation, stirring may be performed until no lumps are left.

<Aging> After gelation, the mixture is aged for a predetermined time.
The aging temperature is preferably 35 ° C. or less, particularly 30 ° C.
The following is preferred. At a temperature exceeding 35 ° C., impurities such as sodalite and A-type zeolite may be generated,
Not preferred. The aging time is not particularly limited, but usually about 24 hours is sufficient.

<Crystallization> The gel aged for a predetermined time is heated to complete crystallization. The crystallization temperature is 85 to 9
It is in the range of 5 ° C. If the temperature is lower than 85 ° C., A-type zeolite may be generated, and if the temperature exceeds 95 ° C., impurities such as P-type zeolite may be generated, which is not preferable. The crystallization time is set at 1 in order to prevent the unreacted gel from remaining without completely crystallizing.
5 hours or more are preferable.

<Washing and Drying> The low-silica X-type zeolite synthesized as described above is filtered, washed sufficiently with water or warm water, and dried by heating. Filtration and washing may be performed using a usual method. Drying can be carried out using a usual method, and the temperature and time can be carried out without any particular limitation as long as the low silica X-type zeolite is dried. For example, a temperature of 90 to 100 ° C.
It is sufficient to dry it to the extent.

<Molding> The low silica X-type zeolite thus obtained is formed into a desired shape, for example, a spherical shape, an elliptical shape, a disk shape, a column shape, etc., with a clay binder or the like, if necessary. It can be. As a molding method, a known method such as rolling granulation and extrusion molding can be used. The size to be molded can be changed depending on the use. In the case of a spherical molded body, the size may be uniformed by classifying the obtained molded body by a sieve. When using a clay binder, if a molded body can be obtained, its amount,
The type is not particularly limited, and examples thereof include attapulgite clay.

<Ion exchange> The low-silica X-type zeolite obtained by the above steps or a molded article thereof is brought into contact with an aqueous solution of a calcium salt such as an aqueous solution of calcium chloride, if necessary, under a constant temperature condition. Exchange with ions. The compound used for ion exchange may be any desired ion exchange species, and can be arbitrarily selected depending on the application. As the exchange method, a batch contact method, a column flow method, or the like is usually used, and can be appropriately selected according to the shape of the low silica X-type zeolite or a molded article thereof. The temperature at which the ion exchange is carried out is determined in consideration of the speed at which the ion exchange equilibrium is reached, but usually about 50 ° C. is sufficient.

<Activation> By activating the ion-exchanged low-silica X-type zeolite obtained by the above steps or its molded body by heat treatment, it is possible to obtain an adsorbent / separating agent having high adsorption performance. . Here, the condition of the activation treatment may be any condition under which moisture in the low silica X-type zeolite or its molded body can be desorbed, and thereby the adsorption performance is improved. For example, it can be achieved by heating at 400 ° C. for about one hour under air flow.

The zeolite bead molded product obtained by the method of the present invention can be used for applications such as an adsorbent separating agent such as selectively adsorbing nitrogen from a mixed gas by an adsorption method to separate and concentrate oxygen.

The low-silica X-type zeolite having a silica / alumina molar ratio of 2.20 to 2.40 obtained by the method of the present invention has high adsorption performance, and exchanges sodium ions with divalent cations such as Ca ions. The reason why they are also excellent in heat resistance is that, based on the study of the present inventors, the crystal skeleton has a faujasite structure while maintaining the faujasite structure like the conventional X-type zeolite or low-silica X-type zeolite having a silica / alumina molar ratio of 2.0. The number of aluminum atoms in the crystal is higher than that of the conventional X-type zeolite and lower than that of the low-silica X-type zeolite having a silica / alumina molar ratio of 2.0, that is, the physical properties as shown in the conventional CaX-type zeolite. It is estimated that That is, the low silica X-type zeolite having a silica / alumina molar ratio of 2.0 has the same properties as the A-type zeolite, and in the case of the Ca ion-exchanged agent, it exists in the β cage (sodalite cage) of the zeolite crystal. Al water which forms the zeolite skeleton during firing is hardly released, and reacts with the water due to heat to separate from the crystal skeleton, thereby changing the crystal structure.
While the adsorption capacity of the adsorption site is significantly reduced, the silica / alumina molar ratio obtained by the method of the present invention is 2.
The low silica X-type zeolite of 20 to 2.40 is unlikely to cause the above-mentioned reaction, which is considered to be a low silica X-type zeolite having a silica / alumina molar ratio of 2.0, because the structural water in the β cage is easily released. It is considered that the structure does not change.

However, such presumption does not restrict the present invention.

[0024]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

The adsorption performance was measured by the nitrogen equilibrium adsorption amount.
The silica / alumina molar ratio was measured by lattice constant, chemical composition, and ²⁹ Si NMR.

-Nitrogen equilibrium adsorption amount-The powder was lightly pressed so that the powder would not be scattered under vacuum conditions and used as a sample for evaluation. The X-type zeolite was weighed out and measured using a Kern-type electronic balance. Activation was performed at 350 ° C. for 2 hours at a degree of vacuum of 10 ⁻³ torr or less as pretreatment conditions. The adsorption temperature was kept at 25 ° C., and the adsorption capacity (unit: Ncc / g) was calculated from the change in weight after a sufficient equilibrium was reached after the introduction of nitrogen gas. The nitrogen adsorption amounts in Examples and Comparative Examples are measured values at an equilibrium pressure of 700 torr.

[0027] The powder is ~ lattice constant ~ measurement sample, X-rays diffractometer (Mac Science Co., Ltd., Model: MXP ³⁾ was used to measure the silicon internal addition method.

-Chemical composition- The powder was dissolved in hydrofluoric acid to prepare a sample for measurement. In the measurement, the sample was measured by ICP emission spectrometry using an inductively coupled plasma emission spectrometer (manufactured by PerkinElmer, model: optima 3000).

²⁹ Si NMR Measurement The powder as a measurement sample was measured using a nuclear magnetic resonance analyzer (Model JX-270, manufactured by JEOL Ltd.).

The compositions of sodium aluminate and sodium silicate used in Examples and Comparative Examples are shown in Table 1.

[0031]

[Table 1]

Example 1 According to the formulation shown in Table 2, sodium aluminate 6
1.8 g (0.386 mol) of purified water 115.2 g
(6.395 mol) and sodium hydroxide 1.8
Solution A in which 2 g (0.0455 mol) was dissolved was allowed to cool to 30 ° C. or lower. Then, 73.8 g of sodium silicate
(0.605 mol) in 115.2 g (6.395) of purified water.
Mol) was allowed to cool to 30 ° C. or lower. Solution B was added at a time while stirring solution A, and stirring was continued for 5 minutes while maintaining the temperature at 30 ° C. or lower until no lumps were present, thereby completing gelation. This was allowed to stand for 24 hours to mature. Next, the temperature was raised to 90 ° C. and maintained at that temperature for 20 hours to complete the crystallization, followed by filtration and washing with a Buchner funnel. This was dried at 90 ° C. for 16 hours.

[0033]

[Table 2]

Table 3 shows N based on the composition of the raw materials in Table 2.
shows a _{a 2 O, Al 2 O 3} , SiO 2, H 2 O molar composition ratio.

[0035]

[Table 3]

The silica / alumina molar ratio of the obtained X-type zeolite was measured by the above method, and the results are shown in Table 4 as the lattice constant, chemical composition and ²⁹ Si NMR measurement results.

[0037]

[Table 4]

Further, the attapulgite clay 10 was added to the obtained X-type zeolite and 100 parts by weight of the X-type zeolite.
A part by weight was added, and the mixture was formed into a spherical shape using a marmellaizer molding machine (manufactured by Fuji Paudal, model: Q-230). Thereafter, a muffle furnace at 600 ° C. for 2 hours (Advantech,
After sintering the clay by firing with a model number: KM-600), calcium chloride (granular, manufactured by Central Glass Co., Ltd.) is used in advance.
Was added to an aqueous solution of calcium chloride dissolved in purified water so as to have a 5-fold equivalent, and the mixture was contacted at 50 ° C. for 3 hours to perform ion exchange to calcium ions. After the obtained molded body was washed and dried, it was activated in a tubular furnace (manufactured by Advantech) at 400 ° C. for 1 hour under air flow to obtain an ion-exchanged molded body. The amount of nitrogen adsorption was measured by the above-mentioned method, and the results are shown in Table 4.

Examples 2 to 4 X-type zeolites were obtained in the same manner as in Example 1 according to the formulations shown in Table 2. Table 3 shows the molar composition ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ , and H ₂ O based on the composition of the raw materials in Table 2. The silica / alumina molar ratio of the obtained X-type zeolite was measured in the same manner as in Example 1, and the lattice constant,
Table 4 shows the chemical composition and ²⁹ Si NMR measurement results.

Further, the same additives and operations as in Example 1 were performed to obtain an ion-exchanged compact. The nitrogen adsorption amount was measured in the same manner as in Example 1, and the results are shown in Table 4.

Comparative Examples 1 to 3 X-type zeolites were obtained in the same manner as in Example 1 according to the formulations shown in Table 2. Table 3 shows the molar composition ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ , and H ₂ O based on the composition of the raw materials in Table 2. The silica / alumina molar ratio of the obtained X-type zeolite was measured in the same manner as in Example 1, and the lattice constant,
Table 4 shows the chemical composition and ²⁹ Si NMR measurement results.

Further, the same additives and operations as in Example 1 were performed to obtain a molded body. The nitrogen adsorption amount was measured in the same manner as in Example 1, and the results are shown in Table 4.

As can be seen from the above results, the silica / alumina molar ratio obtained by the method of the present invention is 2.20.
The low silica X-type zeolite of ~ 2.40 has a large adsorption capacity.

[0044]

As is apparent from the above description, according to the method of the present invention, high-purity low-silica X-type zeolite can be easily produced. The low-silica X-type zeolite synthesized in this manner is used as an adsorbent separator having a large adsorption capacity, as it is or after being formed into a compact, and then subjected to ion exchange with other ions, for example, alkali or alkaline earth. be able to.

Claims (1)

[Claims] 1. 2.4 to 2.7 Na ₂ O.Al ₂ O ₃ .2.
After aging a mixed gel of 7 to 2.8 SiO ₂ · 120 to 140 H ₂ O at a temperature of 35 ° C. or less, the mixed gel is crystallized at a temperature of 85 to 95 ° C., wherein the silica / alumina molar ratio is 2 2. A method for producing a low silica X-type zeolite having a particle size of 20 to 2.40.