JP2921958B2 - Method for producing δ-type alkali metal disilicate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for stably producing a δ-type alkali metal disilicate.

Prior art Among the various crystalline modifications of crystalline sodium silicate of the formula Na ₂ Si ₂ O ₅ , the δ form has the highest cation exchange capacity and is suitable for softening water containing Ca ions and Mg ions, for detergents It is suitable as a builder (see JP-A-60-227895).

As a method for producing such δ-type sodium disilicate, for example, the method of W. Hoffman et al. Is known,
Sodium disilicate can be obtained by simply dehydrating and calcining the aqueous solution of sodium silicate prepared so that iO ₂ / Na ₂ O = around 2 mol.

JP-A-60-161324 discloses that a crystalline silicate is crystallized by mixing an acidic compound such as sulfuric acid or phosphoric acid in a reaction mixture containing an amorphous alkali metal silicate and heating the mixture. Is described. On the other hand, JP-A-61-286215 discloses that when a reaction mixture containing an amorphous alkali metal silicate is heated to crystallize and precipitate a crystalline silicate, an acid such as sulfuric acid or phosphoric acid is added after the start of crystallization. It has been proposed to add compounds. Furthermore, the above two publications describe that by inoculating a crystalline silicate as a seed crystal into the reaction mixture or after the start of crystallization thereof, the purity of the product can be improved and the reaction rate can be increased. Have been.

Further, U.S. Pat.No.4,585,642 discloses that a sodium silicate reaction mixture is dehydrated and calcined until crystallization to produce crystalline sodium silicate, by adding a small amount of crystalline sodium silicate as a seed crystal. It is described that crystallinity can be improved.

Japanese Patent Application Laid-Open No. 63-310717 discloses a method of spray-drying a 20 to 65% by weight water glass solution, then subjecting the solution to pyrothermal crystallization at 500 to 800 ° C., and then pulverizing the solution to produce crystalline sodium silicate. In this case, it is described that crystallization can be enhanced by performing crystallization while returning a part of the pulverized crystallized product to the crystallization step.

However, in these known production methods, α-form and β-form
The type tends to be by-produced, and the δ-type disilicate is obtained as a mixture containing a relatively large amount of these, and as a result, the cation exchange ability is reduced, which is not preferable as a detergent builder. Also, in the above-described known method, by controlling the crystallization temperature and time, by-products such as α-form can be suppressed to some extent, but even in that case, strict control in the crystallization step is required, and the process is also extremely difficult. And the equipment cost increases, which is uneconomical. In addition, if the known method is used, the composition of the obtained crystallized product tends to vary due to fluctuations in the production conditions,
δ-type disilicate cannot be obtained stably.

DISCLOSURE OF THE INVENTION An object of the present invention is to produce δ-type disilicate by a simplified process while suppressing α-type and β-type by-products.

Constitution of the inventionThe method for producing a δ-type alkali metal disilicate of the present invention comprises the steps of:
The molar ratio of O ₂ / M ₂ O (M represents an alkali metal) is 1 to 3
After mixing a boron compound in an amount of 0.05 to 5 mol% based on B ₂ O _{5 with} respect to the silica content (SiO ₂ ) to the aqueous solution of an alkali metal silicate, the mixture is dried and fired.

 Hereinafter, the present invention will be described in more detail.

As the alkali metal silicate, the molar ratio of SiO ₂ / M ₂ O is 1
~ 3, preferably 1.5 ~ 2.5. Here, M is an alkali metal such as sodium or potassium. When the molar ratio is less than 1, the alkali content becomes too large, and α-type disilicate and crystalline monosilicic acid (Na ₂ O · SiO ₂ ) are generated, and δ-type disilicate is not generated. On the other hand, when the SiO ₂ / M ₂ O ratio is 3
When it exceeds, the alkali content is small, cristobalite is easily generated, and δ-type disilicate is hardly generated.

The aqueous alkali metal silicate solution has, for example, the formula Na ₂ O.nSiO
By reacting with NaOH using sodium silicate represented by ₂ , silica gel, colloidal silica, aerosil, or the like, one having a desired SiO ₂ / Na ₂ O molar ratio can be obtained.

Examples of the boron compound to be added to and mixed with the aqueous alkali metal silicate solution include water-soluble compounds such as boric acid, borax and tetraborate.

Boron compound is preferably added in an amount of 0.05 to 5 mol% in B ₂ O ₅ reference the silica content (SiO _2), more preferably from 0.1 to 1 mol%. When this mixing amount is 0.05
When the amount is less than mol%, the effect of adding the boron compound is not sufficiently exhibited. On the other hand, when the content exceeds 5 mol%, the concentration of the boron compound having a low cation exchange ability in the obtained dried and calcined product increases, and accordingly, the concentration of the δ-type disilicate decreases and the cation exchange ability decreases. However, it is not preferable as a detergent builder.

Next, the silicate aqueous solution to which the boron compound has been added is dried, calcined, and crystallized to obtain a δ-type alkali metal disilicate. The δ-type disilicate preferably has a composition of M ₂ O · mSiO ₂ (M: alkali metal, m = 1.7 to 2.5). Known calcination methods can be used as they are, and δ-type disilicate can be stably obtained over a wide range of calcination conditions. The firing temperature is suitably from 500 to 800 ° C, preferably from 650 to 800 ° C, more preferably from 700 to 750 ° C. If the sintering temperature is lower than 500 ° C., crystallization does not sufficiently proceed, while if it exceeds 800 ° C., melting occurs and the crystallization is not sufficient.

Effects of the Invention According to the present invention, a silicate aqueous solution containing a boron compound is dried and calcined to be crystallized, thereby suppressing by-products of other crystal types such as α-type and β-type, and providing a δ-type alkali. Metal disilicate can be produced.

Moreover, in this production method, a δ-type silicate can be obtained without being largely influenced by the composition and crystallization conditions of the raw material silicate, so that stable production becomes possible and the process can be simplified, so that it is industrially possible. It is advantageous.

The δ-type silicate obtained in the present invention has excellent cation exchange ability and is suitable as a builder for detergents.

Hereinafter, the present invention will be described more specifically with reference to examples. Prior to this, the measuring method adopted in the examples will be described.

Measurement method (1) Crystallization rate The obtained crystalline sodium disilicate is subjected to powder X-ray measurement (XRD) under the following conditions.

Measurement conditions Step scan mode Target / filter (monochrome): λCuKα Voltage / current: 40kv, 20mA Start angle: 5deg Stop angle: 50deg Scan width: 0.02deg Count rate: 1kcps Count time: 0.4sec Diverging slit (DS / 1st) 1deg Receiving slit (RS / 2nd): 0.15mm Scattering slit (SS / 3rd): 1deg X-ray diffraction diagram of the sample before crystallization after dehydration at 250 ° C for 1 hour The intensity I ₀ of 2θ = 20 (deg) with respect to the swell is determined, and is set to be 100% amorphous. As crystallization progresses, this amorphous portion decreases,
After the crystallization is completed, it matches the baseline. Taking this point as 0% of amorphous, that is, 100% of crystallization ratio, the base line rise value I (cps) was read at 2θ = 20 (deg) from the X-ray diffraction diagram of crystalline sodium silicate, and the following equation was used. Determine the crystallization rate.

(2) δ-type crystallization ratio When the obtained crystalline silicate is δ + α or δ + β, 100% crystallized product is mixed, and a calibration curve between the compounding ratio and the X-ray intensity ratio is obtained. Then, the ratio of δ-type, α-type or β-type is determined from the X-ray intensity of the crystal to be obtained, and this is multiplied by the crystallization rate to determine the δ-type crystallization rate. Therefore, the δ-type crystallization ratio indicates a value for all silicates.

(3) Crystal Form Joint Joint Committee on Powder Diffraction Standards (Joint Commitee o
n Powder Diffraction Standards, 1975) (α-type Na ₂ Si ₂ O ₅ : File No. 1)
8-1241, β-type Na ₂ Si ₂ O ₅ : File No.23-529, δ-type Na ₂ Si ₂ O ₅ :
For File No. 22-1396), when peaks in which α-type, β-type and δ-type do not overlap each other were determined, the following peaks were preferable.

α-type Na ₂ Si ₂ O ₅ : d = 3.31 (Å) β-type Na ₂ Si ₂ O ₅ : d = 2.97 (Å) δ-type Na ₂ Si ₂ O ₅ : d = 2.83 (Å) Was found, crystals were present. In addition, amorphous (amor.) Was considered to be present when the crystallization ratio for all silicates was less than 100%. Then, the peak intensity was determined for each of the above peaks, and the ratio to the δ-form was used as a measure of the content of α-form and β-form.

(4) Crystallinity The crystallinity of the (111) plane having the highest intensity of the δ type was determined from the relative intensity of the sample when the peak intensity of the sample of Comparative Example 1 was set to I ₀ (111) 100.

Crystallinity (%) = (I ₍₁₁₁₎ / I ₍₁₁₁₎ ) × 100 (5) Cation exchange capacity (CEC) Sample 1 in calcium chloride aqueous solution 1 with CaO concentration of 300 mg /
g (anhydrous equivalent) was added and reacted by stirring at 20 ° C.
After 0 minutes, the sample was separated, and the concentration of residual calcium ions in the liquid was analyzed. From this, the amount of calcium ions adsorbed on the crystalline disilicate was calculated and defined as CEC.

Example 1 In the stainless steel container of Example 15, sodium silicate (SiO ₂ : 2
8.5 wt%, Na ₂ O: 9.55 wt%) (2100 g) is taken, and 95.7 wt% sodium hydroxide (147.5 g) is dissolved to prepare a sodium silicate aqueous solution having a SiO ₂ / Na ₂ O = 2.00 molar ratio. Then separately water
An aqueous boric acid solution in which 6.2 g of boric acid (H ₃ BO ₃ : 100%) is completely dissolved in 500 g is prepared, and this is added to the above-mentioned aqueous solution of sodium silicate and completely dissolved in each other. The amount of boric acid added is 0.5% based on SiO _{2 with} respect to B ₂ O ₅ .

Further, the aqueous solution of sodium silicate is transferred to a hot plate heated to 200 ° C. and dried. Next, after dehydration in a dryer at 250 ° C. for 1 hour, the resultant was transferred to an electric furnace and crystallized at 730 ° C. for 3 hours.

The properties of the obtained crystalline sodium silicate are shown in Table 1 together with Comparative Example 1 below. The X-ray diffraction pattern is shown in FIG.

Comparative Example 1 An experiment was performed under the same conditions as in Example 1 except that boric acid was not added.

The properties of the obtained crystalline sodium silicate are shown in Table-
1 is shown. The X-ray diffraction pattern is shown in FIG.

As is apparent from Table 1, in Example 1 of the present invention, almost no by-products of α-type and β-type were obtained, and only δ-type was obtained. Also, the peak intensity ratio of the δ-type (111) plane is improved, and the crystallinity is improved. Accordingly, the CEC tends to improve.

Example 2 In a beaker of 1, sodium silicate (SiO ₂ : 27.22 wt%,
(Na ₂ O: 12.78 wt%) 250 g was taken, 4.33 g of 95.7 wt% sodium hydroxide was completely dissolved to prepare an aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O = 2.00 molar ratio. Separately, boric acid (H ₃ BO ₃ :
After dissolving 1.41 g of 100%) in 50 g of pure water, it was added to the above sodium silicate aqueous solution, mixed well, and then the mixed aqueous solution was divided into three portions on a hot plate at 200 ° C. and dried. Next, the dried product was placed in a stainless steel vat, transferred to a degreasing furnace at 250 ° C., and dehydrated. The mixing amount of boric acid is
It is 1.0 mol% based on B ₂ O _{5 based on} O ₂ .

After dehydration, pulverized and uniformly mixed, the powder was taken in a crucible and crystallized at a predetermined temperature for 3 hours using an electric furnace. Table 3 shows the properties of the obtained δ-type sodium disilicate.
2 is shown.

Comparative Example 2 The procedure of Example 2 was repeated except that an aqueous solution of silicic acid to which boric acid was not added was used. Table 2 shows the properties of the obtained δ-type sodium disilicate.

In Table 2, in the case of Comparative Example 2 in which sodium silicate containing no boron compound was crystallized, at a temperature of 700 ° C to 740 ° C, a high CEC was obtained.
Above ℃, the crystallization rate of δ-type with respect to the total silicate was extremely reduced, and a material having substantially no CEC was obtained. That is, the temperature range in which the δ-type forms 90% or more is as narrow as 40 ° C.,
Due to the temperature variation during the actual production, crystalline disilicates other than the δ type are produced as by-products, resulting in low CEC, which is not preferable as a detergent builder.

On the other hand, in the case of Example 2 in which a composition containing 1 mol% of a boron compound based on B ₂ O _{5 with} respect to SiO ₂ was crystallized,
Form δ forms over a wide temperature range of 660 ° C to 780 ° C and as high as 120 ° C, and the CEC is high. From this, it is clear that the composition within the range of the present invention has a wide δ-formation temperature range and enables stable production.

Example 3 The same procedure as in Example 1 was carried out except that the amount of boric acid was changed, and the amounts shown in Table 3 below were added to the aqueous solution of sodium silicate, and the firing temperature was changed to 750 ° C.
Type sodium silicate was manufactured and its properties were measured.
It was shown to.

With a composition within the preferred range to which boric acid was added, the δ-type crystallization ratio was improved, and the CEC was also higher. However, when 6 mol% is added based on B ₂ O ₅ , the δ-type crystallization ratio tends to decrease, and the CEC tends to decrease accordingly.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the crystalline sodium silicate obtained in Example 1. FIG. 2 is an X-ray diffraction diagram of the crystalline sodium silicate obtained in Comparative Example 1.

────────────────────────────────────────────────── ─── Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01B 33/20-39/54

Claims (1)

(57) [Claims] 1. An aqueous alkali metal silicate solution having a molar ratio of SiO ₂ / M ₂ O (M represents an alkali metal) of 1 to 3 is mixed with a silica content (SiO ₂ ) on the basis of B ₂ O ₅ . A method for producing a δ-type alkali metal disilicate, comprising mixing 0.05 to 5 mol% of a boron compound, followed by drying and firing.