JPH0581525B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing zeolite using a hydrous amorphous silica as a silica source. More specifically, silica containing 40 to 60% by weight of water, which is produced as a by-product when synthesizing cryolite or aluminum fluoride using silicofluoride (hereinafter referred to as by-product silica), is used as a silica source. Regarding the manufacturing method. The demand for zeolite increased rapidly with the start of incorporating this substance into synthetic detergents, and it has now become the social mission of zeolite manufacturers to produce and supply zeolite at the lowest possible cost.
Zeolites are usually produced by a process consisting of a hydrothermal reaction of a composition consisting of silica, alumina and soda. There are two typical methods for producing zeolite for detergents: One method consists of mixing sodium silicate (water glass) and sodium aluminate in a predetermined ratio and crystallizing the mixture, and the other method involves adjusting the composition of pretreated silicates such as clay minerals. This method consists of crystallizing. In the former case, separate equipment is required to dissolve the silica source and the alumina source in the sodium hydroxide solution. This method allows easy purification of raw materials and allows stable production of zeolite with excellent whiteness and ion exchange ability. Since the reaction production process and operation are complicated, equipment investment and operating costs are likely to be high, and ultimately it is difficult to produce zeolite at a low cost. In the case of the latter, it was developed with the aim of utilizing naturally produced, inexpensive raw materials, from the viewpoint that it does not have the drawback of the former, which is the high cost of raw materials. However, since the raw material is a natural mineral product, it contains undesirable components such as the following: components that interfere with zeolite crystallization;
It may contain many components with poor reactivity or components that deteriorate the physical properties or quality of the product zeolite. Therefore, in the latter method,
In order to increase the purity or reactivity of naturally occurring raw materials, pretreatment of the raw materials, such as acid treatment or pulverization/calcination, is necessary. Therefore, even if the latter method is adopted, the final manufacturing cost will end up being about the same as when the former method is adopted. Amatsusae, zeolite products related to the latter,
The quality tends to be slightly inferior to the former, as it is colored reddish yellow. In view of the above-mentioned state of the known methods for producing zeolite, the present inventors have conducted extensive research into an economical method for producing zeolite particularly suitable for use in synthetic detergents. As a result, we found that the above-mentioned by-product silica has the following characteristics: (1) It is rich in chemical activity, and (2) It easily disperses or dissolves in a low concentration aqueous sodium hydroxide solution at a temperature of about 80°C. When this product is used as a silica source for zeolite production, it is possible to produce zeolite, which is suitable for detergents, at a lower cost using simpler production equipment, which is comparable to the case where sodium silicate, which is a known method, is used as a silica source. Discovering the fact that it can be manufactured at low cost,
We have arrived at the present invention. As is clear from the above description, an object of the present invention is to provide a simple and economical method for producing zeolite by effectively utilizing a specific by-product silica that has not been used much in the past. The present invention has the following main configuration (1) and the following embodiment mechanism (2). (1) Hydrous amorphous silica, aluminum hydroxide, sodium hydroxide, and water, which are produced as by-products when synthesizing cryolite or aluminum fluoride using silicofluoride, are treated as follows (1) to (3). Mix within the molar ratio and mol% range, and store the resulting mixture at normal pressure and 80 to 105℃.
A method for producing zeolite, which is characterized by reacting the zeolite under vigorous stirring and then crystallizing it within the same pressure and temperature range. [Na ₂ O] / [Al ₂ O ₃ ] = 1.5 to 3.0 (1) [SiO ₂ ] / [Al ₂ O ₃ ] = 1.5 to 2.1 (2) [H ₂ O] / [H ₂ O] + [ Na ₂ O〕＋〔Al ₂ O
₃ ] + [SiO ₂ ] × 100 = 90 to 96 mol% (3) (2) Dissolve aluminum hydroxide in an aqueous sodium hydroxide solution, and add hydrated amorphous silica or the substance to the solution obtained by the dissolution. The method according to item 1 above, wherein the suspension is mixed in water or an aqueous sodium hydroxide solution. The structure and effects of the present invention will be explained in detail below. First, the above-mentioned by-product silica used in the present invention is, for example, a by-product during the production of phosphoric acid in the phosphoric acid manufacturing industry, and is a by-product when the recovered fluorine compound is recycled. This material is usually recovered as an aggregate of primary particles having a moisture content of 40 to 60% by weight, a specific surface area of 0.5 to 50 m ² /g, and a particle size of 1 μm or less. In the method of the present invention, it is extremely important to use the by-product silica in the reaction in a hydrated state in order to ultimately produce fine particle zeolite with a large ion exchange capacity. For reference, the following known silicas a to d do not produce favorable results even when used in place of the by-product silica in the method of the present invention for the following reasons. In other words, a. The method disclosed in JP-A-53-56199 (method for manufacturing water glass) in which by-produced silica is used after drying its water content to 5% by weight or less, has a high cost of raw materials. In addition, it causes dust generation or flashing of the dried product, and the product is a powder that is difficult to handle in terms of processing. Furthermore, there is a problem in that the physical properties of the powder prevent its rapid and uniform dispersion when mixed into a sodium hydroxide solution or a sodium aluminate solution for the production of zeolite. a Furthermore, in connection with the invention of the signal, the reactivity of the dried product of silica, which is a by-product obtained by drying a water-containing product at a high temperature that causes loss of its silanol groups, is further reduced with respect to its own sodium hydroxide, etc. Therefore, it is not suitable as a substitute for the by-product silica according to the present invention. b. Substances such as clay silicate and others disclosed in JP-A-54-107899 are
When using the by-product silica according to the present invention, there are completely unnecessary extra steps such as mixing with an aqueous sodium hydroxide solution, aging, dissolving or pulverizing the by-product silica in advance of the reaction with sodium hydroxide. It becomes necessary. c Fine powder amorphous silica such as commercially available Aerosil (manufactured by Nippon Aerosil Co., Ltd.), Nipsil (manufactured by Nippon Silica Co., Ltd.) or silica sol, or d Silica gel or activated silica (Note: Obtained by acid treatment of acid clay). Regarding the former two (note c),
The latter, activated silica, has similar difficulties in terms of processing handling as a powder and raw material cost, but the chemical activity of the reaction for producing zeolite is higher than that of the by-product silica according to the present invention. significantly inferior. It is sufficient that the content of silica in the by-product silica used in the present invention is 90% by weight or more based on drying at 100°C (constant weight product), and it can be preferably used. If the content decreases to less than 90% by weight, the quality of the desired zeolite product may decrease, and depending on the types of coexisting components, the quality of the filtrate from which the zeolite crystals are filtered, which will be described later, may deteriorate. As a result, this may have an undesirable effect when recycling and using the filtrate in carrying out the method of the present invention. Silica containing a large amount of such undesirable coexisting components, particularly coloring organic substances, is particularly undesirable as a raw material for producing zeolite for detergents. The morphological quality or solubility of aluminum hydroxide used in the present invention is determined in accordance with the practice of the present invention. When adopting an embodiment in which by-product silica is mixed, there are no particular limitations. However, in the case of adopting an embodiment in which the substance is mixed with the by-product silica in powder form or by suspending the powder substance in a sodium hydroxide solution, the powder substance is heated at 80° to 105°C. It must be able to dissolve rapidly in the liquid at a temperature of .
Specifically, for example, it is preferable to use α-type aluminum hydroxide having a particle size distribution that substantially passes the entire surface through a water sieve with openings of 44 μm, and which is in the form of fine particles that is highly reactive with sodium hydroxide. When adopting an embodiment in which aluminum hydroxide is mixed with by-product silica in the form of a powder or suspension as in the above-mentioned ○○○, if an aluminum hydroxide with poor reactivity with sodium hydroxide is used, the zeolite synthesis according to the present invention will be difficult. The reaction requires higher temperatures or longer times than normal embodiments of the invention. In addition, since the by-product silica is extremely easily soluble in sodium hydroxide solution, the liquid phase of the reaction temporarily becomes silica-rich in composition, which tends to generate sodalite, which can lead to the loss of the desired product. Zeolite also tends to be of inferior quality. The sodium hydroxide used in the present invention may be fresh each time, but the filtrate obtained by separating zeolite crystals from the match synthesis solution after the previous zeolite synthesis according to the present invention (Note: mother liquor and washing solution) ) and replenishing only the insufficient amount, that is, the amount taken out of the system as a result of the previous reaction, there is no particular problem, and such an embodiment is economically preferable. The sodium hydroxide may be either solid or liquid (note: sodium hydroxide solution). However, the following impurities that may be contained in the sodium hydroxide, i.e. iron content, colors the zeolite. It is preferable that the amount of impurities in the sodium hydroxide be as low as possible for the reason of reducing the strength. Rather than adding water independently, the water used in the present invention is only used as that brought into the reaction system along with the aforementioned recycled filtrate, by-product silica, aluminum hydroxide, and additional sodium hydroxide. Preferably, such an embodiment is one of the characteristic features of the method of the present invention. As a result of using water in the above-described manner, the balance of sodium hydroxide and water in the reaction mixture according to the present invention is maintained within the most preferable range, and it is most economical to maintain it in this way. It is. The compositional ratios of silica, alumina, soda, and water for zeolite synthesis in the present invention are sufficient within the range of known compositional ratios for forming zeolite. To explain this point in more detail, first, regarding the concentration of sodium hydroxide, since the by-product silica according to the present invention has high chemical activity toward sodium hydroxide, the concentration should be determined by using another raw material. It is sufficient to have the ability to dissolve aluminum hydroxide. but,
On the other hand, in many known methods, the crystallization time of zeolite is extended due to a decrease in the concentration of sodium hydroxide used, and conversely, when the concentration is increased, sodalite is more likely to be produced as a by-product. It is similar to The preferred concentration of sodium hydroxide has the following relationship with the order of mixing the raw materials according to the present invention. That is, aluminum hydroxide is more difficult to dissolve than by-product silica in a dilute sodium hydroxide solution. Therefore, if an embodiment is adopted in which aluminum hydroxide is dissolved in a sodium hydroxide solution in advance, additional addition of sodium hydroxide is not necessary for the subsequent dissolution process of by-product silica, which is already produced. Only the sodium hydroxide content remaining in the sodium aluminate solution is sufficient. On the other hand, it is known that the optimum concentration of silica in the production of zeolite depends on the concentration of alumina in the reaction system. Also in the case of the present invention, when the [SiO ₂ ]/[Al ₂ O ₃ ] molar ratio exceeds 2, sodalite is likely to be produced as described above. The concentration of silica and alumina is also related to the size of the primary particles of the zeolite produced, which are larger at lower concentrations;
It tends to be smaller at higher concentrations. From the above explanation and experimental facts, the concentration of each component composition applied to the method of the present invention is preferably within the following range, taking into account the quality of the zeolite to be produced and the manufacturing cost. [Na ₂ O] / [Al ₂ O ₃ ] = 1.5 to 3.0 (molar ratio) [SiO ₂ ] / [Al ₂ O ₃ ] = 1.5 to 2.1 ( ) H ₂ O / [H ₂ O] + [Na ₂ O〕＋〔Al ₂ O ₃ 〕
+[SiO ₂ ]×100=90 to 96 (mol %) The desired zeolite can be produced by any of the following methods for mixing the above-mentioned raw materials in the method of the present invention. That is, they include a method in which by-product silica and aluminum hydroxide are separately dispersed in a sodium hydroxide solution and then mixed together, or a method in which both are simultaneously mixed in a sodium hydroxide solution.
A method in which by-product silica is dissolved after dissolving aluminum hydroxide in a sodium hydroxide solution, a method in which by-product silica is dissolved in a sodium hydroxide solution and then aluminum hydroxide is mixed, or both by-product silica and aluminum hydroxide are mixed. This method involves dissolving the two components separately and then mixing them together. However, when zeolite is synthesized by directly reacting powdered raw materials in a sodium hydroxide solution as in the method of the present invention, the reaction mixture is subjected to severe If stirring is not interrupted, the zeolite produced tends to become aggregated crystals, and 1
The secondary particles also tend to become larger. Furthermore, a major reason is thought to be that aluminosilicate precipitates on the surface of undissolved raw material powder and prevents the dissolution of the raw material, but this precipitation can significantly delay or stop the subsequent reaction. . In such a case, the X-ray diffraction peak of the produced zeolite will be low and the ion exchange capacity will also be low. Incidentally, it is preferable that the sodium hydroxide solution mentioned here includes the above-mentioned liquid that is recycled and used in the zeolite production reaction, and severe stirring is defined as stirring to the extent that the aluminosilicate precipitated on the surface of the undissolved raw material can be peeled off. This indicates the strength of stirring. For example, when stirring vigorously using a homogenizer, it is preferable to stir at a rotation speed of 5000 to 15000 rpm.
In particular, it is preferable to stir at around 10,000 rpm. Because of the above, when attempting to economically produce zeolite of a quality suitable for detergent builders, for example, by using the method of the present invention as a by-product silica source that is extremely easily soluble in a sodium hydroxide solution. The above-mentioned raw material mixing method is used, that is, after dissolving aluminum hydroxide in a sodium hydroxide solution, the wet by-product silica can be mixed directly or after being made into a suspension using a part of the sodium hydroxide solution. The most preferred method is mixing. Regarding this, an explanation using drawings will be added. The figure shows a relationship curve between dissolution time (hours, minutes) of by-product silica in a sodium hydroxide solution and dissolution rate (%). The symbols indicating each curve in FIGS. 1 and 2 indicate the dissolution conditions, that is, the Na ₂ O concentration, [SiO ₂ ]/[Na ₂ O] molar ratio and temperature, and the judgment result (pass or fail). This is summarized in the table below.

[Table] Macroscopic judgment based on five levels: ○, △, ゚Poor, and ×Possibility As is clear from the above, it is clear that if appropriate dissolution conditions are selected, good dissolution results for silica can be obtained within a short time. It is. In addition, the dissolution rate of by-product silica is significantly higher than that of aluminum hydroxide, and in addition, dissolving aluminum hydroxide in a sodium hydroxide solution requires the use of a high-temperature, high-concentration solution. These conditions also explain why the above-mentioned mixing method is preferable. Incidentally, the known method for producing A-type zeolite is
In both the method of mixing the reaction raw materials in a solution state and the method of mixing them in a solid state, the raw material mixture is aged at a temperature of about 60 °C or less for about 1 hour to 1 day, and then kept at a temperature of about 80 °C. A process of crystallization is used. However, in the method of the present invention, there is no need for complicated or delicate temperature control as in the above-mentioned known techniques, and after the completion of the above-mentioned reaction of the present invention, the known crystallization temperature of zeolite, for example 80° to 105°C, is not required. It is sufficient to hold the reaction mixture for at least 3 hours. In particular, when adopting the above-mentioned method of dissolving aluminum hydroxide in the sodium hydroxide solution and then mixing by-product silica with the solution, it is necessary to Since there is no need for complicated temperature adjustment such as "cooling of water → heating for crystallization", there is also the advantage that there is no loss of thermal energy associated with such adjustment. Thus, according to the method of the present invention, type A zeolite can be easily produced through a process accompanied by the following two characteristic effects. The first characteristic effect is
By using the by-product silica, there is no need for special dissolving equipment for the raw material silica, and there is no need for a gel forming step that is carried out in known methods.
In other words, in the method of the present invention, dissolution, reaction, and crystallization of aluminum hydroxide and by-product silica can be performed in the same equipment. The second effect is that by-product silica is treated as a hydrated substance, so
There is no process trouble peculiar to the handling of fine powder, such as dust generation or flashing, which is caused by the drying of silica in known methods. The present invention will be specifically explained below using Examples.

[Table] Example From the hydrated by-product silica, aluminum hydroxide, sodium hydroxide and water shown in Table 1, [Na ₂ O]/
[Al ₂ O ₃ ]=2.7 (molar ratio), [SiO ₂ ]/[Al ₂ O ₃ ]=2.0
(molar ratio), a mixture having a composition of H ₂ O = 94 mol % was prepared. Using a homogenizer, heat this mixture at normal pressure and at a temperature of 90℃.
The mixture was stirred at 10,000 rpm for 2 hours. After that, while maintaining the same pressure and temperature, the stirring speed was reduced to 1000 rpm, stirring was continued for 2 hours, and the obtained zeolite crystals were mixed with No. 5C.
filter paper and washed with warm water. Table 2 shows the physical properties of the obtained crystal. Example Using the same raw materials as in the example, [Na ₂ O]/
[Al ₂ O ₃ ] = 1.7 (mole ratio) sodium aluminate solution (Na ₂ O = 18.0 wt%, Al ₂ O ₃ 4 = 17.4 wt%)
was prepared. After heating this sodium aluminate solution to 90°C, sodium hydroxide, water, and hydrated by-product silica are mixed to form [Na ₂ O] / [Al ₂ O ₃ ] =
2.7 (molar ratio), [SiO ₂ ]/[Al ₂ O ₃ ] = 2.0 (molar ratio)
,
A mixture of H ₂ O = 94 mol % was prepared. Using a homogenizer, maintain this mixture at 90°C.
The mixture was stirred at 10,000 rpm for 30 minutes. Thereafter, the stirring speed was lowered to 1000 rpm and stirring was continued for 2 hours, and the obtained zeolite crystals were suction filtered using No. 5C filter paper and washed with warm water. Table 2 shows the physical properties of the obtained crystal. Comparative Example 1 The same procedure as in Example was carried out except that stirring was performed using a motor stirrer at 600 rpm. Table 2 shows the physical properties of the obtained zeolite. Comparative Example 2 The same procedure as in Example was carried out except that stirring was carried out using a motor stirrer at 600 rpm. Table 2 shows the physical properties of the obtained zeolite.

[Table] Measurement method 1 Crystal type: X-ray diffraction analysis method 2 Primary particle size: Scanning electron microscopy method 3 Average particle size: Light transmission particle size analysis method (D50%) 4 Calcium ion exchange capacity: 100℃ dry sample After dispersing 365 mg in 1000 ml of CaCl ₂ :10 ^-3 moI/l for 15 minutes, Ca in the filtrate was measured by atomic absorption spectrometry and corrected by the value of loss on ignition at 1000°C. .

[Brief explanation of the drawing]

Figures 1 and 2 show relationship curves between the dissolution time (hours and minutes) of by-product silica in a sodium hydroxide solution and the dissolution rate (%).

Claims (1)

[Scope of Claims] 1 Hydrous amorphous silica, aluminum hydroxide, sodium hydroxide, and water, which are by-produced when synthesizing quartzite or aluminum fluoride, etc. using silicofluoride, are synthesized by the following (1) to ( 3) are mixed within the molar ratio and mol% range, the resulting mixture is reacted under vigorous stirring at normal pressure and 80 to 105°C, and then crystallized within the same pressure and temperature range. Characteristic method for producing zeolite. [Na ₂ O] / [Al ₂ O ₃ ] = 1.5 to 3.0 (1) [SiO ₂ ] / [Al ₂ O ₃ ] = 1.5 to 2.1 (2) [H ₂ O] / [H ₂ O] + [ Na ₂ O〕＋〔Al ₂ O
₃ ] + [SiO ₂ ] × 100 = 90 to 96 mol% (3) 2 Dissolve aluminum hydroxide in an aqueous sodium hydroxide solution, and add hydrated amorphous silica or the substance to the solution obtained by the dissolution. The method according to claim 1, wherein a suspension in an aqueous sodium hydroxide solution is mixed.