JPS6121910A - Preparation of molded body of synthetic mordenite having high strength - Google Patents

Abstract

PURPOSE:To improve the mechanical strength of the product by calcining a molded body contg. starting materials comprised of silica source, alumina source, and alkali source, and then crystallizing mordenite in aq. soln. of sodium silicate contg. a specified proportion of SiO2 and Na2O. CONSTITUTION:Starting materials comprised of silica source, alumina source, and alkali source are mixed with water. The mixture is calcined after molding it to a desired shape. Then, the calcined molded body is heated in aq. sodium silicate soln. contg. SiO2 and Na2O in 3.4-4 molar ratio to cause crystallization.

Description

DETAILED DESCRIPTION OF THE INVENTION More specifically, the present invention provides a method for producing a synthetic mordenite molded body having excellent mechanical strength.

Zeolite is a crystalline aluminosilicate containing zeolite water, as shown by its origin from the Greek word "boiling stone", and its composition is generally expressed by the following formula.

zM, zo'A1,03-ysiol-gH,0 (where n is the valence of the cation M, 2 is a number in the range of (L8 to 2, y is a number of 2 or more, 2 is a number of 0 or more) ) Its basic structure is an 8104 tetrahedron with silicon at its center and four oxygen atoms coordinated at its vertices, and an Ago tetrahedron with aluminum at its center instead of silicon.
They are regularly bonded three-dimensionally by sharing oxygen with each other so that the atomic ratio of A1+s t ) is 2.

As a result, a three-dimensional network structure having pores of different sizes and shapes is formed due to the different bonding methods of the tetrahedrons.

Further, the negative charges of the AlO2 tetrahedron are electrically neutralized by bonding with cations such as alkali metals or alkaline earth metals.

In general, the pores formed in this way have a size of 2 to 3 times to more than 10 times, but the metal cations bonded to the AlO4 tetrahedron can be mixed with other metal cations of different size or valence. Pore size can be changed by exchanging ions.

Zeolite can be used as a gas or liquid industrial desiccant that utilizes these pores, or as a molecular sieve that adsorbs and separates molecules in a mixture of two or more molecules, and when metal cations are exchanged with hydrogen ions, it can be used as a solid acid. Because of this, it is widely used as an industrial catalyst that takes advantage of this property.

Mordenite type zeolite consists of 12-membered oxygen rings &
7 X 7. 2 consisting of a pore with the diameter of OX and an 8-membered oxygen ring
, has pores with a diameter of 9 x 5.7 A, but 1
Since the pores each consisting of two-membered oxygen rings are independent, they are characterized by having so-called tunnel-like one-dimensional pores.

The chemical formula of mordenite is generally Ha, 0IIAI, O, .10810.・It is expressed as 6H,0, and its slo, /x, o3 molar ratio is higher than that of conventional zeolites, so it has excellent heat resistance and acid resistance, and is widely used industrially as an adsorbent or catalyst. .

Mordenite-type zeolite is a type of zeolite that occurs naturally, and various methods for its synthesis have been proposed.

Most of them are methods for producing mordenite crystal powder.

When using synthetic mordenite industrially, it is often difficult to use mordenite crystal powder as it is, and it is often difficult to use it as a spherical,
It is common to use a columnar or appropriately shaped molded body.

However, since zeolite crystal powder itself does not have mutual bonding properties, organic and inorganic binders are usually used to impart appropriate plasticity and strength when producing molded bodies. Examples of the inorganic binder include clay minerals such as kaolinite, silica sol, and alumina sol.

However, the mechanical strength of the mordenite molded body produced in this manner may be significantly reduced by severe treatments such as acid treatment and heat treatment during the catalytic process.

Furthermore, even if the mechanical strength is maintained to a certain extent, the zeolite component will not only be diluted by the amount of binder added, but also the binder must be It is necessary to increase the amount. In addition, when these molded bodies are used as catalysts, the fired products such as clay minerals as binders may even cause undesirable side reactions.

For this reason, instead of forming a mordenite molded body by the method described above, a molded body of a raw material mixture is made in advance and then crystallized to create a synthetic mordenite molded body having substantially the same shape as before crystallization. Several methods have already been proposed.

However, the mechanical strength of mordenite molded bodies synthesized by conventional methods is not necessarily sufficient for practical use.

In recent years, the development of adsorbents and catalysts that take advantage of the excellent properties of zeolite has been actively carried out, and their applications are expanding. It is desired to develop a synthetic mordenite molded body with strong mechanical strength that can withstand such usage conditions.

As a conventional method, for example, patent application publication Sho 4O-1a614
In the method disclosed in 2007, emphasis is placed on the conditions for crystallizing mordenite); as no measures have been taken to increase its mechanical strength, it cannot withstand harsh physical and chemical treatments; Furthermore, it has low durability against crushing and abrasion, and its uses are limited. In addition, the patent application was announced in 1973.
In the method disclosed in No. 0-33, 056, the raw material mixture molded body is crystallized without being heat-treated at a high temperature, so the disadvantage is that the mechanical strength of the molded body after crystallization is essentially weak. There is.

The present inventors overcame the drawbacks of these conventional methods and conducted intensive studies on the crystallization conditions for compacts with high mordenite content and high mechanical strength. This led to the development of a method for producing synthetic mordenite molded bodies with mechanical strength.

The present invention will be explained in more detail below.

In the present invention, the molar ratio of each component consisting of a silica source, an alumina source, and an alkali source is slo, /A1. o, -q ~s.

N calls/h1. After preparing a raw material mixture of o, -15 to 15 and the rest being water, it was molded into a desired shape and then fired to obtain a raw material mixture molded body, which was then mixed with silicic acid having a composition of 5iOJNatO-54 to 4. The present invention provides a method for producing a synthetic mordenite molded body having high mechanical strength by heating and crystallizing it in an aqueous soda solution.

In the present invention, it is essential to use sodium silicate having a 5iOy'Na2O ratio of &4 to 4, which is prepared by newly dissolving a silica component in a sodium silicate aqueous solution.

Although it is not clear why the mechanical strength of the crystallized molded body increases when a sodium silicate aqueous solution with a 810, Na, O ratio of 54 or more is used, it is believed that it is largely involved in the crystallization mechanism of mordenite. Conceivable.

The present inventors have arrived at the present invention by conducting studies to improve the strength of crystallized compacts using not only commercially available sodium silicate but also sodium silicate having a high 5iOy'Na2O ratio as described above. SiO without newly dissolved silica
, /Na, O with a ratio of 55 or less, a molded article with high strength cannot be obtained.

The raw materials used in the present invention are not particularly limited, as long as the molar ratio of each component in the mixture is within the above range.

As the silica source, amorphous silica, silica sol, silica gel, naturally occurring diatoms, silicate minerals, etc. are used. Particularly when using natural products, it is effective to remove not only silica sources but also impurities that are undesirable for zeolite production before use.

Aluminum hydroxide is also used as an alumina source.

These include aluminum oxide, sodium aluminate, aluminum sulfate, aluminum nitrate, and naturally occurring aluminosilicate minerals such as kaolinite and montmorillonite.

When a natural raw material is used as the silica source or alumina source, it is necessary to take into account the alumina or silica content contained together with the target components and adjust the content to fall within the above composition range.

Caustic soda or sodium silicate is used as the alkali source. The silica component in sodium silicate must be considered as part of the silica source as described above.

How to mix the above ingredients! Although not limited to TjK,
When molding a raw material mixture into a desired shape, the amount of water required varies depending on the shape and size of the molded object, the type of molding equipment, etc. Generally, the water content is in the range of 40 to 120 inches based on the weight of the raw material mixture on an absolute dry basis. This is undesirable as it may lose its shape or cause mutual adhesion. After adding the optimum amount, each raw material component is mixed so that it becomes uniform. If the mixing is uneven, not only will impurities be more likely to be generated, but the distribution of mordenite crystals and the shape of crystal grains in the compact will also be uneven, resulting in a weakened mechanical strength, so sufficient stirring strength and time are required. is necessary.

The uniformly mixed raw material mixture is then molded into a desired shape. The shape of the molded body when used as an adsorbent or catalyst is generally spherical or cylindrical, but for special purposes, shapes such as cylindrical, prismatic, plate, and honeycomb shapes are used. These shapes can also be molded by combining raw materials within the above composition range.

In addition, in order to increase the viscosity and plasticity of the raw material mixture during molding, reduce friction with molding equipment, and improve moldability, molding aids or lubricants such as carboxymethyl cellulose, stearic acid, alcohols, and surfactants are used. It is also within the scope of the present invention to add fibers, etc. during the raw material mixing process.

Various types of molding equipment are used depending on the shape of the molded product, such as an extrusion type, a tableting type, and a single rotation type.

The raw material mixture formed into a desired shape is then subjected to a firing treatment. For certain limited combinations of raw materials, it is possible to crystallize in a sodium silicate aqueous solution without firing at high temperatures and only by drying to the extent that the attached moisture scatters, but for materials that are not fired at high temperatures, crystallization is possible. The mechanical strength of the molded product after curing is weak.

Therefore, in the method of the present invention, it is preferable to perform firing in an atmosphere of 400° C. or higher. However, if fired at a higher temperature than necessary, the raw material molded body becomes vitrified and the reactivity decreases, so the preferred firing temperature is 500 to 800.
It is 00℃.

5tOv/Na when crystallizing the fired raw material compact
, and the use of sodium silicate having an O ratio of 54 to 4 is a feature of the present invention. S of commercially available sodium silicate aqueous solution
The in,/Nano ratio is in the range of 2-5.

Commercially available No. 1 sodium silicate has a s10s/Na, O ratio of approximately 2.
, for No. 2, the value is approximately 3. For No. 2-5.5, the value is approximately 3.

If the molar ratio of each component in the raw material molded body is within the above range, mordenite will crystallize using any commercially available aqueous sodium silicate solution, but a molded body with high mechanical strength will not be obtained. 5i07If the Na, O ratio is 5 or more, a product that can withstand practical use can be obtained, but the objective of the present invention is to obtain a synthetic mordenite molding that can withstand harsh physical and chemical treatments and has strong durability against crushing and wear. To gain body 5iO1/
It is essential that the Na, O ratio is &4~4, and s t
The higher the O,/N a , o ratio, the higher the strength can be obtained. Two methods are known for producing an aqueous solution of sodium silicate, a wet method and a dry method, but it is generally not possible to obtain a commercially available No. 3 sodium silicate solution with an S i 02/Na, O ratio of 54 or higher. Therefore, by newly dissolving the silica component in the sodium silicate aqueous solution, the 51ot/Na2O ratio is adjusted to 5.4 to 4.

The silica component to be dissolved is not specified, and may be synthetic amorphous solid silicic acid or silica gel obtained from sodium silicate and sulfuric acid, or naturally occurring components such as diatomaceous earth.

Preferably, synthetic amorphous solid silicic acid with good solubility is used.

The amount of the sodium silicate aqueous solution used for crystallization should be at least enough to completely immerse the raw material molded body placed in the container, as long as its concentration is appropriate.

Crystallization is carried out under autogenous pressure in the range 120-20 °C. Crystallization time is about 24-72 hours.

The shape of the molded body after crystallization is substantially the same as that of the fired raw material molded body.

After the crystallization is completed, the molded body is separated from the mother liquor, further washed thoroughly with water or hot water, and dried.) An IJum-type synthetic mordenite molded body is obtained.

The mechanical strength of the obtained molded article can be evaluated by measuring the compressive strength. Compressive strength refers to the strength expressed by the pressure at which the molded product collapses when the molded product is placed on a flat plate and pressure is gradually applied from above.

Compressive strength varies depending on the size and shape of the molded object, so
When comparing, compare items of the same size and shape.

The synthetic mordenite shaped bodies obtained by the method of the invention adsorb sufficient amounts of benzene. Furthermore, it not only maintains its shape even when subjected to ion exchange, acid treatment, heat treatment, etc. under severe conditions, but also can sufficiently withstand use under severe abrasion conditions.

Therefore, it can be converted into H-type by exchanging with adsorbent, ion-exchange agent or ammonium ion and then calcined, or catalyzed by dealuminated H-type by repeated mineral acid treatment and heat treatment. It can be used as a solid acid catalyst.

This will be explained in more detail in Examples below.

Example 1 (granulation molding and firing) 718 g of Joshia kaolin, diatom ±18137, 1/+24 g of sodium silicate (No. 5), and 850 cc of water were thoroughly kneaded in a vertical stirring mixer, and then extruded into an extrusion molding machine. It was molded into a cylindrical shape with a diameter of 1.5 gates. After drying this molded body, it was fired in a firing furnace at 700°C for 1 hour. The heating rate of the firing furnace at this time was 200°C/Hr.

The composition of the raw materials used was as follows. (Unit: wt
%) Example 2.44 (Crystallization) No. 6 sodium silicate 1 having the same composition as that used in Example 1
kg of synthetic amorphous solid silicic acid (manufactured by Nippon Silikani Gyo Co., Ltd., trade name Nip Seal, 810.-92.0chi) 19, 69 was dissolved to give 5iOV/Na, 0-! An aqueous sodium silicate solution of L4 was prepared. In Example 1, the fired molded body 1
119 into the above sodium silicate aqueous solution 2, and 17
Heated under autogenous pressure at 5°C for 42 hours.

Similarly, SiO, /IJa20-55. Aqueous sodium silicate solutions of No. 56 were prepared, and the fired molded bodies were crystallized in each of the sodium silicate aqueous solutions. All of the obtained molded bodies were mordenite containing no impurities.

The powder X-ray diffraction diagram of Example 2 is shown in FIG.

810 of the sodium silicate aqueous solution used for crystallization! /Na,.

The compressive strength and benzene adsorption amount (25° C., 5511118)ig) of the mordenite molded body crystallized were as follows.

5iOv/Na, O pressure resistance (c) Benzene adsorption amount Example 2 54 7.2 a8
15 55 a2
&114 56 a-9! lL5
Comparative Example 1 The molded body 119 fired in Example 1 was heated to StO,/N
a, No. 3 sodium silicate solution 2 of O-52 was crystallized in. The crystallization temperature and time were the same as in Example 2. The strength of the mordenite molded body synthesized by K in this way is &7J
It was c9.

Comparative Example 2 Caustic soda (Na, o-75°9%) 73L09 was added to No. 3 silicate soda 1 and 9, and sto, /na, o ""
2.0 was crystallized. The crystallization temperature for 1 hour was the same as in Example 2.

Under these crystallization conditions, the calcined pellets did not retain their original shape. When the solid matter was measured by powder X-ray diffraction, it was found that most of it was mordenite.

Example 5 173 kg of Joshia kaolin used in Example 1.

Diatomaceous earth 4.55 to 9. Sodium silicate 2.65 to 9 and water 2
．． After sufficiently kneading the 08-gold in a vertical mixer, it was molded into a cylinder with a diameter of 1.5 sieves using an extruder.

This molded body was dried and then fired at 650° C. for 1 hour.

The temperature increase rate at this time was 200°C/Hr.

The fired molded body 1 #c9 was charged with an SiO,/Ha, O-15 sodium silicate aqueous solution 2 in which the synthetic amorphous solid silicic acid used in Example 2 was dissolved, and heated at 175° C. for 42 hours.

The powder X-ray tooth diagram of the obtained compact is essentially the same as that in FIG. 1, and its s to, /a1. o, the ratio was 17.5.

In addition, its compressive strength is &7.9. Benzene adsorption amount (25
The temperature at 955°C (Hg) was 6.8 wt.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction diagram of the powder obtained in Example 2.

Claims (1)

[Claims] (1) In a method of producing a synthetic mordenite molded body by molding a raw material mixture consisting of a silica source, an alumina source, an alkali source, and water and then heating the fired molded body in an aqueous sodium silicate solution, the SiO_2/Na_2O ratio is 3.4～
4. A method for producing a high-strength synthetic mordenite molded body, which comprises crystallizing it in an aqueous sodium silicate solution.