DE4423493A1 - Process for the preparation of a precipitated silica - Google Patents

Description

This invention relates to a method of manufacture a precipitated silica.

Synthetic silica has been playing for many Years as a component of dental care products Role. It is a series of processes for making Silica specifically for use in toothpastes are tailored, known. These procedures are liable procedural disadvantages that are both economical are also not ecologically satisfactory.

In a number of processes, large quantities of Electrolytes are used, which then again need to be washed out to the required To achieve purities of the end products. This creates a significant salt load in the waste water (DE-AS 24 46 038).

In other processes, additional substeps for the preparation of special precipitation templates switched on or additional hydrothermal reaction steps with several insulation levels installed (EP-B 0 317 378).

Document DE-B 14 67 019 describes a method for Manufacture of repeater silica with a Surface of above 200 m² / g known. These Precipitated silica is not for use in toothpastes suitable.

Another disadvantage of known methods is that low space-time yield when precipitating silica through the necessary introduction of a Interruption interval (aging step) or by the Use of dilute reaction components. You get  therefore usually only solids at the end of the Precipitation of about 40-60 g SiO₂ / l (EP-B 0 317 378).

It has now surprisingly been found that it is possible is through a one-step precipitation process Precipitated silicas with high space-time Yield and without the addition of electrolytes.

The invention relates to a method for producing a precipitated silica that has a BET surface area of 10-130 m² / g, a CTAB surface of 10-70 m² / g, one average particle diameter of 5-20 µm, a Cu Abrasion in 10% glycerol dispersion of 4-50 mg and a Thickening behavior in CMC solution (20% dispersion) from 300-3500 mPa · s, which is characterized is that you can get a water supply through Add water glass to a pH of 7.0 to 9.9 or 10.0 to 10.7 is set, alkali silicate (weight module SiO₂: alkali oxide = 2.5-3.9: 1) and a mineral acid at the same time adding the pH between 7.0 and 9.9 or 10.0 to 10.7 constant, with the initial Falling temperature is 50-90 ° C and a Viscosity increase after 25% of the precipitation time at the latest occurs after reaching a silica content of greater than 120 g / l or greater than 150 g / l, preferably 160 g / l to 240 g / l to pH 6, preferably 3.5, the Solid separated by filtration, washes, dries and married.

For filtration you can use chamber presses, band filters or Insert membrane filter presses.

For drying you can use a circulating air dryer, Büttner dryer, current dryer or similar dryer deploy.

You can get the liquefied filter cake in one Dry the spray dryer.  

You can use the filter cake without liquefying one Undergo grinding drying.

The inventive method has the advantage that at high solids content in the precipitation suspension, low Water retention capacity of the filter cake, and consequently that Use of low drying energies, with high Economy a wide range of abrasives in the precipitated silica (and thus when used in Toothpaste in the finished paste) can be set. The degree of abrasiveness can be specifically varied the solids content in the precipitation suspension are, with accompanying changes in precipitation parameters, such as for example temperature, pH or feed rate of the reactants, further variations also with regard to allow the thickening behavior, the refractive index, etc. Despite the variation in the solids content move this in principle in the present precipitation process a very high level (120 g / l, preferably 160 g / l to 240 g / l).

The manufactured according to the inventive method Precipitated silica can be used as an abrasive or Thickening component used in toothpaste formulations become. Another application is use as a polishing or abrasive. Preferably, the Precipitated silica produced according to the invention as Abrasive silica can be used in toothpastes.

Examples

The physico-chemical and application data of the precipitated silicas obtained are in Table 1 listed.

example 1

In a 30-liter precipitation vessel with indirect heating, 12.8 liters of water are introduced with stirring and heated to 85 ° C. While maintaining this temperature, pH 8.5 is first adjusted by adding a little water glass solution (weight module 3.4: 1 = 26.8% SiO₂ and 7.85% Na₂O; density 1.352 g / ml). Thereafter, by simultaneous addition of 56.5 ml / min of water glass (composition as indicated above) and sufficient sulfuric acid (50%) that pH 8.5 is kept constant, it is precipitated for 240 minutes. This suspension is then acidified with sulfuric acid (50%) to pH 3.5. The silica content of the suspension is 171 g / l. The viscosity curve during the precipitation is shown in Fig. 1.

The silica obtained is extracted using a suction filter the suspension separated, the filter cake with water washed, dried at 105-110 ° C and on a laboratory Grind pin mill.

Example 2

The procedure according to Example 1 is followed, with the difference that the pH of the water introduced is adjusted to pH 10.7 using a water glass solution and this pH value is maintained during the simultaneous addition of water glass and sulfuric acid. The silica content of the suspension is 173 g / l. The viscosity curve during the precipitation is shown in Fig. 2.

Example 3

The procedure is as in Example 2. Only the silica content in the suspension is increased to 210 g / l by increased amounts of water glass and sulfuric acid. The viscosity curve during the precipitation is shown in Fig. 3.

Example 4

The procedure of Example 1 is followed, with the difference that the pH 7 is kept constant by adding 56.5 ml / min of water glass and as much sulfuric acid (50%). The felling time is 126 min. After subsequent acidification to pH 3.5, a silica content of 125 g / l is determined. The viscosity curve during the precipitation is shown in Fig. 4.

Example 5

The procedure is as in Example 1, using a water glass with a weight modulus of 2.5 (20.44% SiO₂ and 8.18% Na₂O, d = 1.3012 g / ml) and by increasing the water glass dosage to 107.3 ml / min and H₂SO₄ metering to 26.33 ml / min, a silica content of 160 g / l is set in the suspension. The viscosity curve during the precipitation is shown in Fig. 5.

The methods used are as follows:

• - The determination of the specific nitrogen surface (BET) takes place according to Brunauer - Emmet - Teller with the help the AREA meter from Ströhlein. The Determination takes place according to DIN ISO 5794/1 Annex D. The Original method was first published in "Journal of the America Chemical Society ", 60 (1938) page 309. The Bakeout temperature is 160 ° C for 1 hour.
• - The CTAB surface is formed by adsorption of Cetyltrimethylammonium bromide determined at pH 9 (see Jay, Janzen and Kraus in "Rubber Chemistry and Technology" 44 (1971) 1287).
• - The particle distribution is measured using a Coulter Counter, Model TA II from Coulter Electronics, determined. To the The 100 µm capillary is used.
• - The abrasiveness is determined according to the Cu Abrasion method in 10% glycerine dispersion (157 g Glycerin anhydrous, in which 17 g of silica for 12 min 1,500 rpm with the paddle mixer). The Abrasion is measured by 50,000 double strokes Nylon brushes on copper sheets (electrolyte copper) in the above Dispersion. The mg Cu abrasion is obtained from the differential weighing. Literature: Pfrengle, fats, soaps, Paint 63 (1961) 445-451 and Reng, Dany, Perfumery and Cosmetics 59 (1978) 37-45.
• - The thickening behavior is determined at 20% in a carboxymethyl cellulose solution (50 g PEG 400, 1st kg 87% glycerin, 25 g AKU CMC LZ 855, 925 g water). The at least 1 day but not more than 2 weeks old Test solution is mixed with silica, dispersed and determines the viscosity (Brookfield RVT, spindle 5, 10 Rpm, value after 1 min). The measurement of at 25 ° C  thermostatted mixing takes place immediately, after 0.5 h and after 24 h. The latter is the actual measured value.
• - In addition, the humidity (2 h, 105 ° C, DIN ISO 787 part 2), conductivity (4%), loss on ignition (2 h at 100 ° C, analogous to DIN 55 921).

Claims (5)

1. Process for producing a precipitated silica which has a BET surface area of 10-130 m² / g, a CTAB surface area of 10-70 m² / g, an average particle diameter of 5-20 μm, a Cu abrasion in 10% Glycerin dispersion of 4-50 mg and a thickening behavior in CMC solution (20% dispersion) of 300-3500 mPa · s, characterized in that one to a water reserve, which by adding water glass to a pH of 7.0 is set to 9.9 or 10.0 to 10.7, alkali silicate (weight modulus SiO₂: alkali oxide = 2.5-3.9: 1) and a mineral acid are added simultaneously, the pH between 7.0 and 9 , 9 or 10.0 to 10.7 constant, with the initial falling temperature being 50-90 ° C and an increase in viscosity after 25% of the precipitation time at the latest, after reaching a silica content of greater than 120 g / l or greater than 150 g / l, preferably 160 g / l to 240 g / l to pH 6, preferably 3.5, the solid by h Filtration separates, washes, dries and grinds. 2. The method according to claim 2, characterized in that one for filtration chamber presses or Membrane filter presses. 3. The method according to claim 2, characterized in that one for drying a circulating air dryer, butt dryer Current dryer or similar devices. 4. The method according to claim 2, characterized in that liquefied filter cake in a spray dryer dries. 5. The method according to claim 2, characterized in that the filter cake is subjected to grinding drying.