Preparation of precipitated silicas useful as fillers in silicon matrices
AssigneeRhodia Chimie
InventorsRemi Valero, Jean-Noel Jas, Joel Racinoux, Kyu-Min Hwang, Youn-Kwon Yoo, Soline Daudey
Life of this patent
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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.
Claims33
-32. (canceled)
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.
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.
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.
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 SiO2 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 SiO2 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%.
Dependencies are inferred from the claim text.