Title of Invention

PRECIPITATED SILICA

Abstract

The invention relates to high structure precipitated silica that have been subjected to a short retention drying process, a process to manufacture these and the use thereof. The precipitated silica are characterized by the following physico-chemical characteristics:pH (5% in water) (ISO 787-9) 3-8 BET surface area (DIN 66131) m2/g 400 -600 DBP absorption value (DIN 53601, gi100g 380 -420 in relation to dried substance) Tapped density (ISO 787-11) g/l 100 -200 ALPINE sieve residue> 63 ų (ISO 8130-1) % 0.1 -40

Full Text

The present invention relates to precipitated silicas with a high structure, a process to manufacture the silicas and the use of these silicas. The structure of a silica is understood to be the extent to which its primary particles congregate into secondary particles or, respectively, tertiary particles. The unit used to express the size of the structure is the Brabender dibutyl phthalate (DBP) absorption coefficient. Spray dried precipitated silicas are known and sold, for instance, under the brand name of Sipernat®. The silicas are usually manufactured by precipitating waterglass with sulfuric acid, wherein the entire width of possible precipitation variants can be deployed, as described, for example in EP 00 78 909, US 409 47 71 or US 601 32 34. After precipitation the solid matter is filtered off and the filter cake is then spray dried - if necessary it is re-dispersed by adding an acid. Spray drying allows the manufacture of almost spherical, solid particles with a narrow size distribution range. Silicas with DBP absorption values of up to 380 g/110g are known from EP 0 078 909. According to Example 1 of the present patent application, a silica with 380g/100g DBP absorption value is obtained by spray drying a silica suspension containing 11% solids by weight. According to Example 5 of this application a DBP absorption of 346g/100g is obtained by spray drying a silica suspension containing 16 % solid matter by weight. A similar process is disclosed in US 601 32 34. In this case a silica suspension with pH > 4 and a solids content of more than 18 % by weight was spray dried to form particles with an average particle diameter of more than 150nm and a BET surface area of 100 to 350 m2/g. The known spray dried precipitated silicas can be improved in regard to the DBP absorption value. Surprisingly we discovered that high-structured spray dried silicas with DBP absorption values of more than 380g/100g could be obtained by employing a specific precipitation method. The subject of the present invention are precipitated silicas characterized by the following physico-chemical data: which are characterized in that, while stirring and shearing in a vessel containing water heated to 35 - 45°C, a) water and sulfuric acid are added together within at least 100 minutes, maintaining a phi of 6 - 7, wherein the addition of substances is interrupted for 60 - 120 minutes and when the addition of the substances has been completed a solids content of 36 - 42 g/l sets in b) the solid matter is filtered off, the filter cake is washed and c) the solid material is subjected to a short retention drying process A special variant of the process is characterized by the fact that while stirring a vessel containing water heated to 35 - 45°C, preferably 36 - 40°C and maintaining a pH of 6 - 7 and adding waterglass and sulfuric acid together, while shearing the mixture during the entire precipitation time with a disk agitator installed in addition to the agitator, by interrupting the precipitation for 90 minutes from the 13th to the 103rd minute, after a total precipitation time of 137 minutes, a final silica concentration of 38 to 42 g/l is established in the precipitation suspension, the precipitation suspension is then filtered and washed, the filter cake is dried or liquefied by adding water and/or acid to form a suspension containing 8 - 16% solid matter and this is then spray dried. The short retention time drying in process stage c) can be carried out by liquefying the filter cake to a solids content of less than 18% by weight and spray drying this suspension. In a further variant of the process according to the present invention the short retention time drying process can be carried out by means of a spin-flash drying process on the washed filter cake from process stage b). The pH of the end product is of decisive importance for many applications of the silicas. For instance, if it is used as a carrier material for vitamins, a neutral or weak acidic pH is required. The pH can be modified by subsequently treating the spray-dried silica with a base such as ammonia gas or adjusting the pH of the re-suspended filter cake. Determination of the pH of the silica is carried out on a 5% suspension of spray-dried silica according to ISO 787-9. The process according to the present invention can be carried out in that either the pH of the precipitation suspension is not modified after precipitation or lowered to pH 2 - 5, preferably 3, by adding acid (e.g. sulfuric acid). The solid matter is separated from the suspension by known filtration methods such as a filter press (diaphragm filter press). The filter cake obtained in this way can be dried, for example by using a spin flash dryer. It is also possible to liquefy the filter cake by adding water and/or acid. If acid is used (e.g. diluted sulfuric acid), a pH of In a special embodiment of the process according to the present invention, the product that has been subjected to a short retention drying process is subsequently treated with ammonia gas, or, alternatively, the drying process is carried out in the presence of ammonia gas. Adding ammonia gas increases the pH of the silica and enables higher DBP absorption values. A specified particle size distribution can be adjusted with the aid of a spray dryer or a jet dryer (jet tower). This can be adjusted by selecting the dryer type (single material jet, 2 material jet, gas/liquid jet, atomizing disk) and the spraying pressure. Typically a dryer with an atomizing disk is used. Silicas according to the present invention can be used as a carrier for transferring liquids into powder form, e.g. in the crop protection, pesticide and animal feed industries (e.g. vitamin A and E, choline chloride) as a free-flow or anti-caking agent, for example for table salt or instant meals, as well as in elastomers such as tires. The silicas according to the present invention can be used to manufacture catalyst carriers. The following examples will be used to describe the invention without limiting the scope of protection. Reference example 1 Precipitation is carried out according to EP 0 078 909, Example 1. For this purpose 60 m3 of water at a temperature of 40°C were added to a precipitation vessel, fitted with an EKATO MIG agitator and an additional EKATO shearing turbine. Commercially available waterglass (26.8% Si02; 8.0% Na20; density 1.346) and sulfuric acid (96%) flow into this vessel simultaneously at a speed of 10 m3/h and 0.9 m3/h respectively. After the 13th minute of precipitation the addition of waterglass and acid is interrupted for 90 minutes. During this time both stirring organs continue to operate. From the 103rd minute the waterglass and acid are added once more, at the above-mentioned rates, untif the 146th minute. The solids content of the precipitation suspension is 47g/l. The suspension is filtered in filter presses, washed and the resulting filter cake is liquefied under the effects of shearing. The solids content is 11.0%, the pH is 5. The silica suspension is then spray dried. A DBP absorption value of 355g/110g was determined for the product that was obtained in the above manner. The characteristics of the unground product can be found in the table. Reference example 2 The precipitated silica was manufactured according to EP 0 078 909, example 5 and only differs from reference example 1 in the manufacture of the silica suspension for spray drying. The filter cake is adjusted to a solids content of 16% by weight and a pH of 4.5 by adding water and acid under shearing conditions. The DBP absorption value is 349g/100g. The characteristics of the unground product can be found in the table. Example 1 60 m3 of water at a temperature of 38°C were added to a precipitation vessel, fitted with an EKATO MIG agitator and an additional EKATO disk agitator (350 mm diameter). While maintaining apH of 6.5, commercially available waterglass (27.1% Si02; 8.07% Na20; density 1.355) and sulfuric acid (96%) flow into this vessel simultaneously at a speed of 10 m3/h and 0.9 m3/h respectively. The acid is made to flow over the disk agitator, which is started when precipitation begins. After 13 minutes precipitation time, the addition of waterglass and acid is interrupted for 90 minutes. During this time both the agitator and the EKATO disk agitator continue to operate. After this time the waterglass and acid are added once more, at the above-mentioned rates and maintaining the above-mentioned pH for a further 34 minutes. The suspension is then acidulated to pH 3 by adding sulfuric acid. The solids content of the precipitation suspension is 40g/l. The suspension is subsequently filtered and washed in filter presses. For the further processing stage the filter cake is liquefied under shearing conditions by adding water and small quantities of sulfuric acid. The pH is 5.0; the solids content is 12%. The silica suspension is then spray dried. The free sulfuric acid in the material is neutralized downstream of the spray dryer with ammonia gas. The characteristics of the unground product can be found in the table. Example 2 The precipitated silica is manufactured according to Example 1. Deviating from this, the filter cake obtained after processing in the diaphragm filter press is liquefied under shearing conditions by adding water and small quantities of sulfuric acid. The pH is 5.0 and the solids content is 11.0%. The silica suspension is then spray dried. Example 3 The precipitated silica is manufactured according to Example 1. Deviating from this, the filter cake obtained after processing in the diaphragm filter press is liquefied only by adding wafer. The solids content is 8%. The characteristics of the unground product can be found in the table. Example 4 The precipitated silica is manufactured according to Example 1. Deviating from this, the filter cake obtained after processing in diaphragm filter presses with a solids content of 18% is dried for further processing in a spin flash dryer. (O.T. KRAGH, Keramische Zeitschrift, Vol. 30, issue 7, pp 369 - 370, 1978; T. HOEPFFNER, Informations Chemie, Vol. 342, pp 141 - 145,1992). The characteristics of the unground product can be found in the table. Example 5 The precipitated silica is manufactured according to Example 1. Deviating from this the precipitation suspension is not acidulated after precipitation is complete. The suspension is filtered in diaphragm filter presses and washed with highly diluted sulfuric acid with a pH of 1.6 to 1.8. For further processing the filter cake with a solids content of 18% is dried in a spin flash dryer. The free sulfuric acid contained in the material from the washing process is neutralized by adding ammonia, or, alternatively, the pH in the powder is raised to 7.7. The characteristics of the unground product can be found in the table. Example 6 The manufacture of the precipitated silica and the subsequent processing of the suspension, including washing are carried out according to Example 4. For further processing the filter cake is liquefied by adding water under shearing conditions. The pH is 3.2; the solids content is 11%. To neutralize the free sulfuric acid, the material is neutralized with ammonia gas downstream of the spray dryer. The characteristics of the unground product can be found in the table WE CLAIM : 1. A Precipitated silica, characterized by the following physico-chemical characteristics: 2. The precipitated silica as claimed in claim 1, wherein by the following physico- chemical characteristics: 3. The precipitated silica as claimed in claim 1, wherein by the following physico- chemical characteristics; 4. The precipitated silica as claimed in claim 1, wherein by the following physico- chemical characteristics: 5. A process for manufacturing a precipitated silica as claimed in one of claims 1 to 4, wherein, while stirring and shearing in. a vessel containing water heated to 35 - 45°C, a) water and sulfuric acid are added together within at least 100 minutes, maintaining a pH of 6 - 7, wherein the addition of substances is interrupted for 60 - 120 minutes and when the addition of the substances has been completed a solids content of 36 - 42 g/l sets in b) the sohd matter is filtered off, the filter cake is washed and c) the solid material is subjected to a short retention drying process. 6. The process for manufacturing a precipitated silica as claimed in claim 4, wherein the short retention time drying process in process stage c) is carried out by liquefying the filter cake to a solids content of less than 18% by weight and by spray drying this suspension. 7. The process for manufacturing a precipitated silica as claimed in claim 4, wherein the short retention time drying process in process stage c) is carried out by drying the filter cake by means of a spin flash dryer. 8. The process as claimed in any one of claims 5 to 7, wherein the silica obtained after the short retention drying process is adjusted to pH 7 to 8 with ammonia gas. 9. The process as claimed in any one of claims 5 to 9, wherein the filter cake is washed with diluted sulfuric acid. 10. Composition comprising precipitated silica as claimed in any one of claims 1 to 4 as a carrier and animal feed or vitamins or catalysts.

Documents:

0957-mas-2001 abstract-duplicate.pdf

0957-mas-2001 abstract.pdf

0957-mas-2001 claims-duplicate.pdf

0957-mas-2001 claims.pdf

0957-mas-2001 correspondence-others.pdf

0957-mas-2001 correspondence-po.pdf

0957-mas-2001 description (complete)-duplicate.pdf

0957-mas-2001 description (complete).pdf

0957-mas-2001 form-1.pdf

0957-mas-2001 form-18.pdf

0957-mas-2001 form-26.pdf

0957-mas-2001 form-3.pdf

0957-mas-2001 form-5.pdf

0957-mas-2001 petition.pdf