Process for preparing precipitated silicas

Patent metadata

Field	Value
Publication number	US-9550682-B2
Application number	US-201214367455-A
Country	US
Kind code	B2
Filing date	Dec 19, 2012
Priority date	Dec 23, 2011
Publication date	Jan 24, 2017
Grant date	Jan 24, 2017

Abstract

A silica production method comprising reacting a silicate with at least one acid, in which the acid used in at least one of the steps of the production method is a concentrated acid, preferably selected from the group consisting of sulfuric acid having a concentration of at least 80% by weight, in particular at least 90% by weight, acetic acid having a concentration of at least 90% by weight, formic acid having a concentration of at least 90% by weight, nitric acid having a concentration of at least 60% by weight, phosphoric acid having a concentration of at least 75% by weight, and hydrochloric acid having a concentration of at least 30% by weight.

First claim

The invention claimed is:

1. A process for preparing silica, the process comprising:
reacting a silicate with at least one acid according to the following successive steps such that a precipitate is formed:
(i) forming an aqueous stock with a pH of between 2 and 5,
(ii) simultaneously adding silicate and an acid to said aqueous stock to form a reaction medium, such that the pH of the reaction medium is maintained between 2 and 5,
(iii) stopping the addition of the acid used in step (ii) while continuing the addition of silicate to the reaction medium until a pH value in the reaction medium of between 7 and 10 is obtained,
(iv) simultaneously adding silicate and an acid to the reaction medium, such that the pH of the reaction medium is maintained between 7 and 10, and
(v) stopping the addition of the silicate used in step (iv) while continuing the addition of the acid used in step (iv) to the reaction medium until a pH value of the reaction medium of less than 6 is obtained;

separating the precipitate, to obtain a suspension of precipitated silica; and
drying the suspension of precipitated silica,

wherein, in step (ii), a dilute acid is added for x minutes, followed by the addition of a concentrated acid selected from the group consisting of sulfuric acid with a concentration of at least 80% by weight, acetic acid with a concentration of at least 90% by weight, formic acid with a concentration of at least 90% by weight, nitric acid with a concentration of at least 60% by weight, phosphoric acid with a concentration of at least 75% by weight, and hydrochloric acid with a concentration of at least 30% by weight, wherein x is between 10 and 25.

2. The process as claimed in claim 1 , wherein, in step (ii), the concentrated acid is used after reaching a gel point in the reaction medium.

3. The process as claimed in claim 1 , wherein x is between 15 and 25.

4. The process as claimed in claim 1 , wherein the acid used in at least one of the steps (iv) and (v) is a concentrated acid selected from the group consisting of sulfuric acid with a concentration of at least 80% by weight, acetic acid with a concentration of at least 90% by weight, formic acid with a concentration of at least 90% by weight, nitric acid with a concentration of at least 60% by weight, phosphoric acid with a concentration of at least 75% by weight, and hydrochloric acid with a concentration of at least 30% by weight.

5. The process as claimed in claim 1 , wherein the acid used in steps (iv) and (v) is a concentrated acid selected from the group consisting of sulfuric acid with a concentration of at least 80% by weight, acetic acid with a concentration of at least 90% by weight, formic acid with a concentration of at least 90% by weight, nitric acid with a concentration of at least 60% by weight, phosphoric acid with a concentration of at least 75% by weight, and hydrochloric acid with a concentration of at least 30% by weight.

6. The process as claimed in claim 1 , wherein said concentrated acid is sulfuric acid with a concentration of at least 80% by weight.

7. The process as claimed in claim 1 , wherein said concentrated acid is sulfuric acid with a concentration of between 90% and 98% by weight.

8. The process as claimed in claim 1 , wherein a maturation step is performed between step (iii) and step (iv).

9. The process as claimed in claim 1 , wherein a maturation step is performed after step (v).

10. The process as claimed in claim 1 , wherein, in step (v), the addition of the silicate is stopped while continuing the addition of the acid to the reaction medium until a pH value in the reaction medium of between 3 and 5.5 is obtained.

11. The process as claimed in claim 1 , wherein, between step (iii) and step (iv), an acid is added to the reaction medium, the pH of the reaction medium after this addition being between 7 and 9.5.

12. The process as claimed in claim 1 , wherein the entire reaction is performed between 70 and 95° C.

13. The process as claimed in claim 1 , wherein the entire reaction is performed at a constant temperature.

14. The process as claimed in claim 1 , wherein step (i) comprises the addition of an acid to water so as to obtain a pH value in the aqueous stock thus formed of between 2 and 5.

15. The process as claimed in claim 1 , wherein step (i) comprises adding an acid to a water+silicate mixture so as to obtain a pH value said aqueous stock thus formed of between 2 and 5.

16. The process as claimed in claim 1 , wherein step (i) comprises adding an acid to a stock containing preformed silica particles at a pH above 7, so as to obtain a pH value in said aqueous stock thus formed of between 2 and 5.

17. The process as claimed in claim 1 , wherein said drying is performed by atomization.

Assignees

• Rhodia Operations

Inventors

• Clouin Malika
• Neveu Sylvaine

Classifications

• C01B33/128 Primary

  by acidic treatment of aqueous silicate solutions · CPC title

• C01B33/193

  of aqueous solutions of silicates · CPC title