Process for preparing precipitated silica using a mixer or extruder

Abstract

A process for preparing precipitated silica comprising a reaction of a silicate with an acidifying agent to obtain a suspension of precipitated silica (S1), followed by a separation step to obtain a cake, a disintegration step of said cake to obtain a suspension of precipitated silica (S2), and a drying step of this suspension, wherein the disintegration step is performed by mixing using a twin-screw mixer or by extrusion.

Claims

1. A process for preparing a precipitated silica, the process comprising: reacting a silicate with an acidifying agent to obtain a suspension of precipitated silica (S1), followed by separation to obtain a cake having a dry matter content of at least 25% by weight, compacting the cake at a pressure higher than 10 bars and lower than 60 bars; disintegrating the cake to obtain a suspension of precipitated silica (S2) by mixing in a twin-screw mixer or by extrusion, and drying the suspension of precipitated silica (S2).

2. The process according to claim 1, wherein the disintegrating is performed in a twin-screw mixer.

3. The process according to claim 1, wherein the disintegrating is performed in an extruder.

4. The process according to claim 3, wherein the disintegrating is performed in a twin-screw extruder.

5. The process according to claim 1, wherein the cake has a dwell time in the mixer or extruder of less than 10 minutes.

6. The process according to claim 1, wherein the disintegrating is conducted in the presence of an aluminum compound.

7. The process according to claim 1, wherein the cake has a dry matter content of between 25% and 40% by weight.

8. The process according to claim 1, wherein the cake is compacted at a pressure of at least 20 bars.

9. The process according to claim 1, further comprising de-agglomerating the cake prior to disintegrating the cake.

10. The process according to claim 1, wherein the separation consists of filtration, optionally followed by washing.

11. The process according to claim 10, wherein the filtration is performed using a vacuum filter or filter press.

12. The process according to claim 1, wherein the drying is performed by atomization.

13. The process according to claim 1, wherein the product derived from drying is subjected to grinding.

14. The process according to claim 1, wherein the product derived from drying is subjected to agglomerating.

15. The process according to claim 13, wherein the product derived from grinding is subjected to agglomerating.

16. The process according to claim 1, wherein the cake has a dwell time in the mixer or extruder between 20 seconds and 5 minutes.

17. The process according to claim 1, wherein the cake has a dry matter content between 25% and 35% by weight.

18. The process according to claim 1, further comprising de-agglomerating the cake after compacting the cake and prior to disintegrating the cake.

19. The process according to claim 1, wherein the step of compacting the cake is performed on a filter equipped with compacting means.

Description

EXAMPLES

Example 1 (According to the Invention)

(1) The suspension of precipitated silica used (S1) was a slurry of Z1165MP silica derived from a precipitation reaction having the following characteristics: Temperature: 60 C. pH: 4.4-5.2 Humidity: 90%

(2) Part of the suspension of silica S1 was filtered and washed on a filter press and then compacted at a pressure of 8 bars. The resulting silica cake G1 had a dry extract of 23.5%.

(3) The other part of the silica suspension S1 was filtered and washed on a filter press and subjected to compacting at a pressure of 25 bars. The resulting silica cake G2 had a dry extract of 29%.

(4) The cake G1 was de-agglomerated by passing through a Nibbler (Gericke) equipped with an 8-mm screen.

(5) The broken-up silica cake was then added via a metering screw feeder at 5 kg/h to a Clextral BC21 twin-screw extruder rotating at 250 rpm. Sodium aluminate was added via a branch line into the extruder after the feed zone (10 cm distant from the intake) so that the flow rate of sodium aluminate was 0.33 ml/min.

(6) The product leaving the extruder was collected in a tank in which the pH was adjusted to 6 with addition of sulphuric acid.

(7) The slurry obtained was then dried by atomization to provide a precipitated silica in powder form P1.

(8) The cake G2 was de-agglomerated by passing through a Nibbler (Gericke) equipped with an 8-mm screen.

(9) The broken-up silica cake was then added via a metering screw feeder at 5 kg/h to a Clextral BC21 twin-screw extruder rotating at 250 rpm. Sodium aluminate was added via a branch line into the extruder after the feed zone (10 cm distant from the intake) so that the flow rate of sodium aluminate was 0.4 ml/min.

(10) The product leaving the extruder was collected in a tank in which the pH was adjusted to 6 through the addition of sulphuric acid.

(11) The slurry obtained was then dried by atomization to provide a precipitated silica in powder form P2.

(12) It was found, for the slurry obtained from cake G2, that the energy savings were 25% and the associated productivity gain was 33% compared with the drying of the slurry derived from cake G1.

(13) With the process of the invention, it is therefore also possible to obtain very satisfactory results for cakes having a high dry extract.

Example 2 (According to the Invention)

(14) The suspension of precipitated silica used (S1) was a slurry of Z1165MP silica derived from a precipitation reaction, having the following characteristics: Temperature: 60 C. pH: 4.4-5.2 Humidity: 90%

(15) Part of the silica suspension S1 was filtered and washed on a filter press and then compacted at a pressure of 8 bars. The resulting silica cake G1 had a dry extract of 23.5%.

(16) The other part of the silica suspension S1 was filtered and washed on a filter press and then compacted at a pressure of 25 bars. The resulting silica cake G2 had a dry extract of 29%.

(17) Part of the silica cake G1 was broken-up by passing through a Nibbler (Gericke) equipped with an 8-mm screen.

(18) The broken-up silica cake was added via a metering screw feeder at 76 kg/h (corresponding to a specific flow rate of the cake i.e. a rate calculated as per the effective volume of the mixer of 97.4 kg/h/L) to a twin-screw UCP 2*17 mixer (RPA process) rotating at 105 pm. Sodium aluminate was added via a branch line of the mixer after the feed zone so that the flow rate of sodium aluminate was 4.65 ml/min.

(19) The mixed product was collected in a tank in which the pH was adjusted to 6.2 through the addition of sulphuric acid.

(20) The slurry obtained was dried by atomization to obtain a precipitated silica in the form of micro-pearls MP1.

(21) The silica cake G2 de-agglomerated up by passing through a Nibbler (Gericke) equipped with a 8 mm screen.

(22) The broken-up silica cake was then added via a metering screw feeder at 127 kg/h to a twin-screw UCP 2*17 mixer (RPA process) rotating at 155 rpm. Sodium aluminate was added via branch line of the mixer after the feed zone so that the flow rate of sodium aluminate was 9.80 ml/min.

(23) The mixed product was collected in a tank in which the pH was adjusted to 6.2 through the addition of sulphuric acid.

(24) The slurry obtained was dried by atomization to obtain a precipitated silica in the form of micro-pearls MP2.

(25) It was found that for the slurry obtained from cake G2 the energy savings were 25% and the associated productivity gain was 33% compared with the drying of the slurry derived from cake G1.

(26) With the process of the invention it is therefore possible also to obtain very satisfactory result for cakes with a high dry extract.

Example 3

(27) Part of the silica cake G1 obtained in Example 2 was placed in a vessel under continuous agitation for one hour at a specific cake feed rate i.e. a rate calculated as per the effective volume of said vessel of 1.78 kg/h/L, i.e. a much lower rate than in Example 2 for cake G1, the sodium aluminate also being added at a rate of 14.75 g/min to said vessel under agitation.

(28) The product obtained was collected in a tank in which the pH was adjusted to 6.7 through the addition of sulphuric acid.

(29) The slurry obtained was dried by atomization to obtain a precipitated silica in the form of micro-pearls MP3.

(30) It was found that the silica MP1 obtained in Example 2 displayed characteristics close to those of silica MP3, in particular similar dispersibility.