KR970005188B1 - Process for the preparation of precipitated silica - Google Patents

Abstract

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Description

Method of producing precipitated silica

1 to 5 are the viscosity curves during sedimentation in Examples 1 to 5, respectively.

The present invention relates to a method for producing precipitated silica.

Synthetically prepared silica has long played an important role as a component of dental care products. In particular, a series of preparation methods are known for preparing silicas for use in toothpaste. Both of these methods have processing drawbacks that make them both economically and ecologically unsatisfactory.

In one such type of method, a large amount of electrolyte is used, which must be washed again and again to obtain the required purity of the final product. This causes significant salts to be incorporated into the effluent (see DE-AS 24 46 038).

Other methods include additional partial steps to prepare certain initial settling mixtures or additional hydrothermal reaction steps with several separation steps (see EP-B 0 317 378).

A method for producing reinforced precipitated silica having a surface area of at least 200 m 2 / g is known from DE-B 14 67 019. This precipitated silica is not suitable for use in toothpaste.

A further disadvantage of the known methods is the low space-time yield during precipitation due to the need for the introduction of a stationary interval (aging step) or by the use of dilution reaction components. In this way only about SiO2 40 to 60 g / A replacement content of is usually obtained (EP-B 0 317 378).

It has now been surprisingly found that precipitated silica can be produced in a single sedimentation step with high disclosure yields without the addition of an electrolyte.

The present invention simultaneously adds alkali silicate (SiO 2: weight modulus of alkali oxide = 2.5 to 3.9: 1) and mineral acid to an initial amount of water adjusted to a pH value of 7.0 to 9.9 or 10.0 to 10.7 by adding water glass. The pH value is kept constant at 7.0 to 9.9 or 10.0 to 10.7 (wherein the initial settling temperature is maintained at 50 to 90 ° C. and the viscosity increase occurs after 25% of the settling time), and the pH is lower than 6, preferably To 3.5, once the silica content is 120g / Or 150g / Greater than, preferably 160 g / To 240 g / Upon reaching a solid, the solid is filtered off, crushed, dried and pulverized, with a BET surface area of 10 to 130 m 2 / g, CTAB surface area of 10 to 70 m 2 / g and an average particle diameter of 5 to 20 And a Cu abrasion of 4 to 50 mg in a 10% glycerol dispersion and a thickening behavior of 300 to 3500 mPa · s in a CMC solution (20% dispersion).

Chamber presses, belt filters or membrane filter presses can be used for filtration.

For drying, circulating air dryers, Buttner dryers, flow dryers or similar dryers can be used.

The liquefied filter cake can be dried in a spray drying furnace.

The filter cake can be mill dried without liquefaction.

An advantage of the process according to the invention is that the wear properties of the precipitated silica (and thus the final paste when used in toothpaste) can be extensively adjusted with some water retention in the settling suspension and hence less use of energy for drying. The degree of wear can be adjusted as intended by changing the solids content of the settling suspension, where the accompanying settling parameters, such as, for example, temperature, pH value or rate of addition of the reactants, may cause further changes in thickening behavior and control rate. Allow. Despite changes in the solids content, these are generally very high levels (≥120 g / , Preferably ≥160 g / To 240 g / ).

Precipitated silica prepared using the process according to the invention can be used as abrasion or thickening component in toothpaste formulations. It can also be used as a grinding or grinding agent. Precipitated silica prepared according to the invention can preferably be used as abrasive silica in toothpastes.

Example

Physical, chemical and application data regarding the precipitated silica obtained are shown in Table 1.

Example 1

Water 12.8 30 heated indirectly Is introduced into a settling vessel and heated to 85 ° C. with stirring. pH is a small amount of water glass solution (weight modulus 3.4: 1 = 26.8% SiO 2 and 7.85% Na 2 O; density 1,352 g / ) And initial adjustment to 8.5 while maintaining its temperature. Then water glass (composition as mentioned above) for 5 minutes 56.6 m Precipitation is carried out by simultaneous addition of a sufficient amount of (50%) sulfuric acid to keep / min and the pH constant at 8.5. This suspension is then acidified to pH 3.5 with (50%) sulfuric acid. The silica content of the suspension is 171 g / to be. Viscosity curves during settling are shown in Table 1.

The resulting silica is separated from the suspension using a vacuum filter, the filter cake is washed with water, then dried at 105-100 ° C. and ground in a laboratory pin mill.

Example 2

The same method as in Example 1 is used, except that the pH of the water is adjusted to 10.7 using a waterglass solution and the pH is maintained while simultaneously adding waterglass and sulfuric acid. The silica content of the suspension is 173 g / to be. The viscosity curves during sedimentation are shown in Table 2.

Example 3

The same method as in Example 2 is used. The only difference is that the silica content of the suspension is increased to 210 g / To increase. Viscosity curves during settling are shown in Table 3.

Example 4

Water glass 56.6m The same method as in Example 1 was used except that pH was maintained at 7 by adding / min and sufficient (50%) sulfuric acid. Settling time is 126 minutes. After acidification to pH3,5, the silica content was 125 g / Appeared to be. Viscosity curves during settling are shown in Table 4.

Example 5

The same method as in Example 1 was used, wherein the weight ratio was 2.5 (20.44% SiO 2 and 8.18% Na 2 O, d = 1.3012 g / m ), The silica content in the suspension is 160 g / l by increasing the water glass-feed rate to 107.3 ml / min and raising the H2SO4 feed rate to 26.33 ml / min. Viscosity curves during settling are shown in Table 5.

The method used for this purpose is as follows:

Determination of nitrogen specific surface area (BET) is carried out according to Brunauer-Emmett-Teller using Stahlein's AREA-meter apparatus. Measurements are carried out in accordance with DIN ISO 5794/1, Appendix D. The original method was first described in the Journal of the American Chemical Society, 60 (1983), page 309. The control temperature is at 160 ° C. for 1 hour.

CATB surface area is determined by absorption of cetyltrimethylammonium bromide at pH 9 (Jay, Janzen Kraus in Rubber Chemistry and Technologt 44 (1971), 1287).

Particle distribution is measured using a TA II Coulter Counter model from Coulter Electronics. 100 ml capillary tube is used.

Wear characteristics were measured using Cu abrasion in a 10% glycerol dispersion (157 g of anhydrous glycerol with 17 g of silica dispersed for 12 minutes at 1,500 rpm using a paddle stirrer). Abrasion is measured by moving the nylon brush back and forth 50, 000 times on the Cu sheet (copper electrolyte) in the dispersion described above. Cu abrasion is determined by weight difference (Pfrengle, Fette, Seifen, Anstrichmitte 63 (1961) 445-451 and Reng, Dany parfmerie and Kosmetik 59 (1978), 37-45).

Thickening run is measured at 205 in carboxymethyl cellulose solution (50 g PEG 4400, 1 kg 87% glycerol, 25 g AKU CMC L2 855, 925 g water). The test solution, which is at least one day or less than two weeks old, is combined with silica and dispersed, and the viscosity is then measured (Brofield RVT, spindle 5, 10 prm, value after 1 minute). The mixture maintained at a temperature of 25 ° C. is measured immediately after 0.5 and 24 hours. The latter is the actual measure.

-The moisture content (2h, 105 ° C, DIN ISO 7877 part 2), conductivity (4%), loss of ignition (2h at 100 ° C, similar to DIN 55 921) are also measured.

Claims (6)

Alkali silicates (SiO2: weight modulus of alkali oxides = 2.5 to 3.9: 1) and mines are added simultaneously to the initial amount of water adjusted to pH value of 7.0 to 9.9 or 10.0 to 10.7 by addition of water glass [while adding maintain a constant pH value of 7.0 to 9.9 or 10.0 to 10.7 (where the initial settling temperature is maintained at 50 to 90 ° C. and the viscosity increases after 25% of the settling time); After adjusting, once the silica content exceeds 120 g / l or 150 g / l, the solids are separated by filtration, washed, and then dried and pulverized, characterized by a BET surface area of 10 to 130 m ² / g and CTAB. Sedimentation with a surface area of 10 to 70 m ² / g, an average particle diameter of 5 to 20 ml, a Cu abrasion of 4 to 50 mg in a 10% glycerol dispersion and a thickening behavior of 300 to 3500 mPa.s in a CMC solution (20% dispersion). Method of making silica. The method of claim 1 wherein the filtration is carried out using a chamber press or a membrane filter press. The method of claim 1, wherein the drying is performed using a circulating air dryer, butt dryer, flow dryer, or the like. The method of claim 1, wherein the liquefied filter cake is dried in a spray dryer. The method of claim 1 wherein the filter cake is mill dried. The method of claim 1 wherein the pH is adjusted to 3.5 and the silica content reaches 160 to 240 g / l.