High-structured precipitated silicic acids

Description of the invention

The invention relates to highly structured precipitation silicas, a method for their preparation and the use of such silicas.

The structure of silicic acid is understood to mean the extent to which its primary particles are integrated into secondary particles or third-order aggregates. The Brabender method for determining the dibutylphthalate absorption coefficient was adopted as a measure of the structure.

Spray-dried precipitation silicas are known and are commercially available, e.g. under the name Sipernat^®. The silicas are prepared in a known manner by precipitating water glass with sulfuric acid, and a whole range of possible precipitation variants can be used, as described, for example, in EP 0 078 909, US 4,094,771, US 6,013,234 or US 4,495,167.

After precipitation, the solids are filtered off and the filter cake is re-dispersed with the addition of acid if necessary, and then spray dried. Spray drying produces nearly spherical solids with a narrow size distribution.

EP 0 078 909 discloses silicic acids with a dibutylphthalate absorption of up to 380 g / 100 g. According to example 1 of this patent application, a silicic acid is obtained with a dibutylphthalate absorption of 380 g / 100 g. 11 wt.% solids. According to example 5 of this application, in the atomization of a silicic acid suspension containing 16 wt. an absorption of dibutylphthalate of 346 g / 100 g is obtained.

A similar process is disclosed in US 6,013,234. A silicic acid slurry with a pH value> 4 and a solids content greater than 18% by weight. is spray-dried in particles with an average diameter above 150 μm and a BET surface of 100-350 m²/ g.

The known spray-dried precipitation silicas are suitable for improvement in their dibutylphthalate uptake.

It has surprisingly been found that highly structured silicas with a dibutylphthalate absorption above 380 g / 100 g can be obtained by specific precipitation methods.

The subject of the invention is highly structured precipitation silicic acid, which is characterized by having the following physicochemical data:

pH value (5% in water) (ISO 787-9) 3-8 BET surface (DIN 66131) m²/ g 400-600 dibutylphthalate absorption (DIN 53601, referred to dried substance) g / 100 g 382-420 compacted density (ISO 787-11) g / l 100-200 residue on ALPINE sieve> 63 μm (ISO 8130 -1)% 0.1-18

Highly structured precipitation silicas with such data are hereinafter referred to as form l.

Preferably, in particular embodiments of the present invention, the precipitated silicic acid has the following physico-chemical data:

<td>Variety</td><td>II</td><td>III</td><td>IV</td>

<td>pH value (5% in water) (ISO 787-9)</td><td> 3-8</td><td> 3-8</td><td> 3-8</td>

<td>BET area (DIN 66131) m²/ g</td><td> 400-600</td><td> 400-600</td><td> 400-600</td>

<td>absorption of dibutylphthalate (DIN 53601,</td><td></td><td></td><td></td>

<td>with regard to dried substance) g / 100 g</td><td> 382-420</td><td> 382-420</td><td> 382-420</td>

<td>compacted density (ISO 787-11) g / l</td><td> 140-200</td><td> 120-180</td><td> 100-130</td>

<td>residue on ALPINE sieve&gt; 63 μm</td><td></td><td></td><td></td>

<td>(ISO 8130-1)%</td><td> 10-18</td><td> 1-10</td><td> 0,1-1</td>

The subject of the invention is also a method of producing highly structured precipitated silicic acid, characterized in that during mixing and shearing, into a receiver heated to 35-45 ° C made of water

a) water glass and sulfuric acid are simultaneously added over a period of at least 100 min while maintaining the pH 6-7, the feed is stopped for 60-120 min, and after the feed is completed, the solids concentration is adjusted to 36-42 g / l;

b) the solids are filtered and the filter cake is rinsed; and

(c) the solids are dried for a short time, the precipitating silicic acid having the following physico-chemical data:

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<td>Variety</td><td>l</td><td>II</td><td>III</td><td>IV</td>

<td>pH value (5% in water) (ISO 787-9)</td><td> 3-8</td><td> 3-8</td><td> 3-8</td><td> 3-8</td>

<td>BET area (DIN 66131) m²/ g</td><td> 400-600</td><td> 400-600</td><td> 400-600</td><td> 400-600</td>

<td>absorption of dibutylphthalate g / 100 g (DIN 53601, based on dried substance)</td><td> 382-420</td><td> 382-420</td><td> 382-420</td><td> 382-420</td>

<td>compacted density (ISO 787-11) g / l</td><td> 100-200</td><td> 140-200</td><td> 120-180</td><td> 100-130</td>

<td>residue on ALPINE sieve&gt; 63 μm (ISO 8130-1)%</td><td> 0,1-18</td><td> 10-18</td><td> 1-10</td><td> 0,1-1</td>

It is preferable that the short-term drying in step c) is carried out by liquefying the filter cake to a solids content of less than 18% by weight. and the suspension is spray dried.

More preferably, the short-term drying in step c) is carried out by drying the filter cake with a centrifugal flash dryer.

The silicic acid obtained after the short-term drying is preferably adjusted to a pH value of 7-8 by means of gaseous ammonia.

The filter cake is preferably washed with dilute sulfuric acid.

The highly structured precipitation silicic acid according to the invention is used as a food carrier, vitamins or catalysts, as a free-flow or anti-caking agent, as an auxiliary for pulverizing liquids, also used in elastomer mixtures and for the preparation of catalyst carriers. .

According to another variant, the method is characterized in that, during mixing, heated to 35-45 ° C, preferably 36-40 ° C receiver of water maintaining pH 6-7 by simultaneous supply of water glass and sulfuric acid and providing shear by means of a disk agitator installed in addition to the agitator for the entire precipitation time for 90 minutes, precipitation interval from 13 to 103 minutes after complete precipitation time 137 min, the final concentration of silicic acid in the precipitation suspension is set in the range of 38-42 g / l, the precipitation suspension is filtered, rinsed, The filter cake is dried and, with the addition of water and / or acid, suspended at 8-16% solids and spray dried.

Drying for a short time can be carried out in step c), wherein the filter cake is liquefied to a solids content of less than 18% by weight. and the suspension is spray dried.

In another variant of the method according to the invention, the short-term drying is carried out by centrifugal flash drying of the washed filter cake from step b).

The pH of the end product is of decisive importance for many applications of silicic acid. When used as a vitamin carrier, a neutral or slightly acidic pH of the end product is required. The change in the pH value can occur either by post-treating spray-dried silicic acid with a base such as ammonia gas or by appropriately adjusting the pH of the resuspended filter cake.

The determination of the pH value is carried out with 5% by weight. spray-dried silicic acid slurries according to ISO 787-9.

The process of the invention can also be carried out such that either the pH of the precipitation suspension is unchanged after precipitation or it is reduced by adding acid (e.g. sulfuric acid) to a pH of 2-5, preferably of about 3.

The separation of the solids from the slurry is carried out by known filtering operations, e.g. in a filter press (membrane filter press). The filter cake thus obtained can be dried, for example, with a spin flash dryer. It is also possible to liquefy the filter cake with the addition of water and / or acid. When using acids (e.g. dilute sulfuric acid) the pH of the suspension is adjusted to &lt;5, preferably 2-4.

In a particular embodiment of this method, the short-term dried product is then treated with ammonia gas or the drying is carried out in the presence of ammonia gas.

The addition of gaseous ammonia increases the pH value of the silicic acid and allows greater absorption of the dibutylphthalate.

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A specific grain size distribution can be set by means of a spray dryer or a nozzle dryer (nozzle tower). This is possible by selecting the type of dryer (single nozzle, twin nozzle, gas / liquid nozzle, spray plate) and the spray pressure to be used. Typically, a spray disk dryer is used.

As mentioned above, the silicas according to the invention can be used as carriers for pulverising liquids, e.g. in the production of plant protection products, pest control agents and in the production of feed (e.g. vitamins A and E, choline chloride), as release agents. , to improve flow or anti-caking properties, e.g. for table salt or ready meals, and in elastomers, e.g. in tires.

The silicas according to the invention can be used for the preparation of catalyst supports.

The invention is described in more detail in the examples with reference also to comparative examples from the prior art.

Comparative example 1

Precipitation is carried out according to EP 0 078 909, example 1. For this purpose, 60 m are placed in a sedimentation tank equipped with an EKATO MIG agitator and an additional EKATO shear turbine.³ water at 40 ° C. This content is brought simultaneously with a speed of 10.0 m³/ h commercially available water glass (26.8% SiO2, 8.0% Na2O, density 1.346) and sulfuric acid (96%) at a speed of 0.9 m³/ h. After 13 minutes of precipitation, the feed of water glass and acid is interrupted for 90 minutes. During this time, both mixing elements are still moving. From 103 minutes, the water glass and sulfuric acid feed is continued at the above-mentioned speed until 146 minutes. The solids content of the precipitation suspension is 47 g / l.

The slurry is filtered on a filter press, washed and the resulting filter cake liquefies under the action of shear. The solids content is 11.0%, the pH is 5. The silicic acid suspension is then spray dried. The dibutylphthalate absorption was determined to be 355 g / 100 g on the prepared product. The parameters of the unground product are given in the table.

Comparative example 2

The production of the precipitated silicic acid is carried out according to EP 0 078 909, example 5, and differs from comparative example 1 only in the preparation of a silicic acid suspension for spray drying. The filter cake is brought under shear by adding water and sulfuric acid to a solids content of 16% by weight. and to a pH of 4.5. The absorption of dibutylphthalate is 349 g / 100 g. The parameters of the unground product are given in the table.

Example 1

60 m is placed in the precipitation tank equipped with the EKATO MIG agitator and additionally with the EKATO disk agitator (diameter 350 mm).³ water at 38 ° C. This content is adjusted by keeping the pH at 6.5 and at the same time 10.0 m³/ h of commercially available water glass (27.1% SiO2; 8.07% Na2O; density 1.355) and 0.9 m³/ h sulfuric acid (96%). The acid is fed in through a disk agitator, which is started at the beginning of precipitation. After 13 minutes of precipitation, the feed of water glass and acid is interrupted for 90 minutes. During this time, the EKATO agitator and disk agitator are still in operation. The feed of water glass and sulfuric acid is then continued while maintaining the above-mentioned speed and the pH value for a further 34 min. Finally, the slurry is acidified by further feeding of sulfuric acid. The solids content of the precipitation suspension is 40 g / l.

The suspension is then filtered with a filter press and washed. For further processing, the filter cake is liquefied under shear with the addition of water and a little sulfuric acid. The pH is 5.0 and the solids content is 12.0%. Finally, the silicic acid suspension is spray dried. In order to neutralize the free sulfuric acid, the material is neutralized with ammonia gas downstream of the spray dryer. The parameters of the unground product are given in the table.

Example 2

The production of the precipitated silicic acid is carried out as in Example 1. However, the filter cake obtained after treatment in the membrane filter press is liquefied under shear and with the addition of water and a small amount of sulfuric acid. The pH value is 5.0. The solids content is 11%. Finally, the silicic acid suspension is spray dried.

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Example 3

The production of the precipitated silicic acid is carried out as in Example 1. However, the filter cake produced by washing in the filter press is liquefied only with the addition of water. The solids content is 8%. The parameters of the unground product are given in the table.

Example 4

The production of the precipitated silicic acid is carried out as in Example 1. However, the filter cake obtained after treatment in the 18.0% solids membrane filter press is dried before further processing in a centrifugal flash dryer (OT Kragh, Keramische Zeitschrift, Vol. 30, issue 7, pp. 369-370, 1978; T. Hoepffner, Informations Chemie, vol. 342, pp. 141-145, 1992). The parameters of the unground product are given in the table.

Example 5

The production of the precipitated silicic acid is carried out as in Example 1. However, the precipitation suspension is not acidified after completion of precipitation. The suspension is then filtered on a membrane filter press and washed with strongly dilute sulfuric acid, pH 1.6-1.8. The filter cake with a solids content of 18.0% is dried in a centrifugal flash dryer prior to further processing. The free sulfuric acid obtained by the scrubbing is neutralized by adding gaseous ammonia or the pH value of the powder is further increased up to 7.7. The parameters of the unground product are given in the table.

Example 6

The production of the precipitated silicic acid and the processing of the slurry including acid rinsing are carried out according to Example 4. For further processing, the filter cake is liquefied under shear and by the addition of water. The pH value is 3.2 and the solids content is 11%. In order to neutralize the free sulfuric acid, the material is neutralized with ammonia gas downstream of the spray dryer. The parameters of the unground product are given in the table.

Table

<td colspan="2" rowspan="2"></td><td colspan="2">Examples comparative</td><td colspan="10">Examples 1-6 according to the invention</td>

<td> 1</td><td> 2</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td colspan="5"> 6</td>

<td>PH value</td><td></td><td> 6,4</td><td> 6,2</td><td> 7,6</td><td> 6,7</td><td> 6,7</td><td> 6,4</td><td> 3,1</td><td> 4,7</td><td> 6,3</td><td> 7,0</td><td> 7,7</td><td> 6,3</td>

<td>Absorption dibutylphthalate</td><td>g / 100 g</td><td> 355</td><td> 349</td><td> 389</td><td> 382</td><td> 400</td><td> 387</td><td> 383</td><td> 391</td><td> 398</td><td> 406</td><td> 412</td><td> 387</td>

<td>Charge density</td><td>g / l</td><td> 180</td><td> 182</td><td> 154</td><td> 154</td><td> 135</td><td> 120</td><td> 119</td><td> 115</td><td> 111</td><td> 108</td><td> 111</td><td> 164</td>

<td>ALPINE SR&gt; 63 μm</td><td> %</td><td> 10</td><td> 23</td><td> 15</td><td> 1,4</td><td> 1,8</td><td> 0,3</td><td> 0,2</td><td> 0,3</td><td> 0,3</td><td> 0,2</td><td> 0,1</td><td> 18</td>

<td>BET area</td><td>m²/ g</td><td> 429</td><td> 515</td><td> 454</td><td> 458</td><td> 485</td><td> 484</td><td> 501</td><td></td><td></td><td></td><td> 476</td><td> 495</td>

<td>Suspension</td><td>PH</td><td colspan="2"> ~ 6</td><td colspan="4"> ~ 3</td><td colspan="6"> ~ 7</td>

<td>Wash</td><td></td><td colspan="2">indifferent</td><td colspan="4">indifferent</td><td colspan="6">sour</td>

<td>Filter cake slurry</td><td>PH</td><td> 5</td><td> 4,5</td><td> 5</td><td> 5</td><td> 5</td><td>falls off</td><td>falls off</td><td colspan="4">(the cake has a pH of ~ 3)</td><td> 3,2</td>

<td>Solids content</td><td> %</td><td> 11</td><td> 16</td><td> 12</td><td> 11</td><td> 8</td><td> 18</td><td colspan="5"> 18</td><td> 11</td>

<td>Addition of NH₃</td><td> -</td><td> -</td><td> +</td><td> -</td><td> -</td><td> -</td><td> -</td><td> +</td><td> +</td><td> +</td><td> +</td><td> +</td><td> +</td>

<td>Dryer</td><td>SP</td><td>SP</td><td>SP</td><td>SP</td><td>SP</td><td>SF</td><td>SF</td><td>SF</td><td>SF</td><td>SF</td><td>SF</td><td>SF</td><td>SP</td>

* SF = Centrifugal Shot Dryer SP = Spray Dryer

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