Process for preparing precipitated silica comprising a high compaction step

Abstract

A process for preparing precipitated silica comprising a reaction of a silicate with an acidifying agent to obtain a suspension of precipitated silica, followed by a step of separation to obtain a cake and a step of drying said cake, wherein a step of compaction of said cake at a pressure greater than 10 bars is carried out between the step of separation and the step of drying.

Claims

1. A process for preparing precipitated silica, the process comprising; reacting a silicate with an acidifying agent to obtain a precipitated silica suspension, separating a precipitated silica from the suspension by a single separating step to obtain a cake, wherein the separating step consists of filtration, optional washing, and compacting on a filter press, and drying the said cake, wherein compacting said cake is carried out at a pressure between 10 and 45 bars and wherein, after compacting and before drying, said cake has a dry matter level between 29 and 35 wt %.

2. The process according to claim 1, wherein compacting said cake is carried out at a pressure between 15 and 45 bars.

3. The process according to claim 1, wherein compacting said cake is carried out at a pressure of at least 20 bars.

4. The process according to claim 1, not comprising a disintegrating step.

5. The process according to claim 1, wherein the drying step is not carried out by atomization.

6. The process according to claim 1, further comprising a lump breaking step which is carried out between the compacting step and the drying step.

7. The process according to claim 1, wherein the dried cake is subjected to a grinding step.

8. The process according to claim 1, wherein the dried cake is subjected to an agglomerating step.

9. The process according to claim 1, wherein compacting said cake is carried out at a pressure between 20 and 35 bars.

10. The process according to claim 1, wherein, after compacting and before drying, said cake has a dry matter level between 29 and 32 wt %.

11. The process according to claim 7, wherein the dried cake that has been subject to the grinding step is subjected to an agglomerating step.

Description

EXAMPLES

Example 1 (Reference)

(1) The precipitated silica suspension used (S) is a Z1165MP silica slurry, resulting from a precipitation reaction, having the following characteristics: Temperature: 60 C. pH: 4.4-5.2 Humidity: 90%

(2) The silica suspension S is filtered and washed on a filter press, then undergoes compacting at a pressure of 8 bars on the same filter. The resulting silica cake has a solids content of 23.5 wt %.

(3) The silica cake is then lump broken by passing through a Nibleur tool (Gericke) equipped with an 8 mm grate.

(4) The lump-broken silica cake is then fed into a ring dryer (GEA Barr Rosin) by a conveyor belt at 8 kg/h. The input temperature of the dryer is set at 305 C. and the output temperature at 130 C.

(5) The output product is a precipitated silica in powder form with a humidity equal to 6.4%.

(6) The obtained precipitated silica has a pore distribution such that its pore volume ratio V2/V1 (pore volume consisting of the pores with diameters comprised between 175 and 275 /pore volume consisting of the pores with diameters smaller than or equal to 400 , the pore volumes being measured by mercury porosimetry, the pore diameters being calculated by the Washburn relationship with a contact angle theta equal to 130 and a surface tension gamma equal to 484 dynes/cm or N/m (Micromeritics Autopore IV 9500 porosimeter)) is 54%.

Example 2 (According to the Invention)

(7) The precipitated silica suspension S is filtered and washed in the same way as in example 1.

(8) At the end of washing, compacting at a pressure of 25 bars by inflating membranes of the membranous plates of the filter press is applied to the cake. The silica cake obtained has a solids content of 30 wt %.

(9) The silica cake is then lump-broken by passing through a Nibleur tool (Gericke) equipped with an 8 mm grate.

(10) The lump-broken silica cake is then fed into a ring dryer (GEA Barr Rosin) by a conveyor belt at 9 kg/h. The input temperature of the dryer is set at 300 C. and the output temperature at 131 C.

(11) The output product is a precipitated silica in powder form with a humidity equal to 7.1%.

(12) An energy gain of 29% can be seen, as well as an associated productivity gain of 39% relative to example 1.

(13) In addition to having a pore volume ratio V2/V1 (56%) close to that of the precipitated silica obtained in example 1, the precipitated silica also has a similar dispersibility to the latter.

(14) The process according to the invention here comprising a compacting step at a pressure of 25 bars makes it possible to save energy and increase productivity during drying.