Preparation of precipitated silicas useful as fillers in silicon matrices

Abstract

Carboxylic acids are employed during the preparation of precipitated silica or a suspension of precipitated silica to provide precipitated silicas with low water uptake, which are useful, for example, as reinforcing fillers for silicon matrices.

1 .- 32 . (canceled) 
   
   
       33 . A process for the preparation of a precipitated silica or of a precipitated silica suspension, comprising mixing a carboxylic acid with or adding same to the filtration cake resulting from the reaction of precipitation of the silica, before or during the disintegration of the filtration cake, the resulting mixture subsequently being optionally dried. 
   
   
       34 . The process as defined by  claim 33 , whereby enhancing the properties of the silica as filler for solid organosilicon matrices. 
   
   
       35 . The process as defined by  claim 33 , in which said carboxylic acid is selected from among maleic acid, formic acid, octanoic acid, acetic acid, oxalic acid, propionic acid or succinic acid. 
   
   
       36 . The process as defined by  claim 33 , in which said carboxylic acid is selected from among maleic acid, formic acid, octanoic acid, propionic acid or succinic acid. 
   
   
       37 . A process for the preparation of a precipitated silica or of a precipitated silica suspension, comprising:
 reacting at least one silicate with at least one acidifying agent, to produce a precipitated silica suspension,   filtering said precipitated silica suspension, to provide a filtration cake, and   disintegrating said filtration cake,   
     and which also comprises mixing at least one carboxylic acid with said filtration cake or adding said at least one carboxylic acid thereto, either before or during the disintegration operation, the mixture obtained subsequently being optionally dried. 
   
   
       38 . The process as defined by  claim 37 , in which said carboxylic acid is selected from among maleic acid, formic acid, the octanoic acid, acetic acid, oxalic acid, propionic acid or succinic acid. 
   
   
       39 . The process as defined by  claim 37 , in which said carboxylic acid is selected from among maleic acid, formic acid, octanoic acid, propionic acid or succinic acid. 
   
   
       40 . A precipitated silica prepared by the process as defined by  claim 37 . 
   
   
       41 . The precipitated silica as defined by  claim 40 , having a content of carboxylic acid+corresponding carboxylic, expressed as carbon, of at least 0.02% by weight. 
   
   
       42 . The precipitated silica as defined by  claim 40 , having at its surface, molecules of said carboxylic acid and/or molecules of the carboxylate corresponding to said carboxylic acid. 
   
   
       43 . A precipitated silica suspension prepared by the process as defined by  claim 37 . 
   
   
       44 . A precipitated silica having:
 a water absorption lower than 6%,   a level of residual anion, expressed as alkaline metal sulfate, of less than 1% by weight,   a content of carboxylic acid+corresponding carboxylate, expressed as carbon, of at least 0.02% by weight.   
   
   
       45 . The precipitated silica as defined by  claim 44 , having a water uptake of greater than 3%. 
   
   
       46 . The precipitated silica as defined by  claim 44 , having a level of residual anion, expressed as alkaline metal sulfate, of less than 0.5%. 
   
   
       47 . The precipitated silica as defined by  claim 44 , having a content of carboxylic acid+corresponding carboxylate, expressed as carbon, of at least 0.03% by weight. 
   
   
       48 . The precipitated silica as defined by  claim 44 , having at its surfaces thereof, molecules of carboxylic acid and/or molecules of the carboxylate corresponding to a carboxylic acid. 
   
   
       49 . The precipitated silica as defined by  claim 48 , wherein said carboxylic acid is maleic acid, formic acid, octanoic acid, acetic acid, oxalic acid, propionic acid or succinic acid. 
   
   
       50 . The precipitated silica as defined by  claim 48 , wherein said carboxylic acid is maleic acid, formic acid, octanoic acid, propionic acid or succinic acid. 
   
   
       51 . The precipitated silica as defined by  claim 44 , having a CTAB specific surface of from 50 to 260 m 2 /g. 
   
   
       52 . The precipitated silica as defined by  claim 44 , having a DOP oil uptake of greater than 300 ml/100 g, preferably of greater than 310 ml/100 g. 
   
   
       53 . The precipitated silica as defined by  claim 44 , having a mean particle size or a median particle diameter of less than 30 μm. 
   
   
       54 . The precipitated silica as defined by  claim 44 , having a pH from 3.5 to 7.5. 
   
   
       55 . The precipitated silica as defined by  claim 44 , having a BET specific surface and a CTAB specific surface such that the BET specific surface-CTAB specific surface difference is at most 60 m 2 /g. 
   
   
       56 . The precipitated silica as defined by  claim 44 , in the form of a powder. 
   
   
       57 . A process for the preparation of a precipitated silica comprising the following stages:
 (a) providing a starting aqueous vessel heel with a temperature of from 80° to 100° C. and which comprises a silicate, the concentration of silicates in said starting vessel heel, expressed as SiO 2  equivalent, being less than or equal to 15 g/l,   (b) adding an acidifying agent to said starting vessel heel, at a temperature of from 80° to 100° C., to adjust the pH of the reaction medium to a value of from 7 to 8,   (c) adding a silicate and an acidifying agent, optionally simultaneously, to the medium thus produced, at a temperature of from 80° to 100° C., the respective amounts of silicate and of acidifying agent, added over time being such that, throughout the duration of the addition:   the pH of the reaction medium remains from 7 to 8, and   the concentration of silicate in the medium, expressed as SiO 2  equivalent, is less than or equal to 35 g/l,   (d) adding an acidifying agent to the medium obtained, at a temperature of from 80° to 100° C., to adjust the pH of the medium to a value of from 3 to 6.5,   (e) filtering the suspension of silica,   (f) drying the filtration cake obtained on conclusion of the filtration (e), said process further comprising, prior to the drying thereof in stage (f), mixing the filtration cake, or adding thereto, at least one carboxylic acid, and the filtration cake thus obtained exhibiting prior to drying thereof in stage (f), a loss on ignition at 1000° C. of greater than 80%.   
   
   
       58 . The process as defined by  claim 57 , further comprising:
 (g) milling or micronizing the silica obtained on conclusion of stage (f).   
   
   
       59 . The process as defined by  claim 57 , wherein the drying stage (f) is carried out by atomization. 
   
   
       60 . The process as defined by  claim 57 , wherein the filtration cake obtained on conclusion of the filtration (e) is subjected, prior to the drying thereof in stage (f), to a disintegration operation, the carboxylic acid being added to said cake before or during said disintegration operation. 
   
   
       61 . The process as defined by  claim 57 , wherein said carboxylic acid is selected from among maleic acid, formic acid, octanoic acid, acetic acid, oxalic acid, propionic acid or succinic acid. 
   
   
       62 . The process as defined by  claim 57 , wherein said carboxylic acid is selected from among maleic acid, formic acid, octanoic acid, propionic acid or succinic acid. 
   
   
       63 . A reinforcing filler for an organosilicon matrix comprising the precipitated silica prepared by the process as defined by  claim 57 . 
   
   
       64 . A shoe sole, polyamide matrix, elastomeric matrix, cement or concrete composition, liquid carrier, dentifrice composition or battery separator comprising the reinforcing filler as defined by  claim 63 .