Patent ID: 8252261
Filing Date: 2012-08-28
Classification: C01B

Abstract:
1. A process for the preparation of finely divided precipitated silica having 66 percent or more of particles of size less than 10 μm, the process comprising the steps of: (i) preparing a dilute solution of sodium silicate in at least two parts having a silica concentration in the range of from 40 g to 70 g SiO (ii) adjusting the sodium ion concentration to be in the range of from 0.45 to 1 mole per liter of a first part of the silicate solution of step (i) by adding a sodium salt; (iii) providing a dilute mineral acid solution having a concentration in the range of from 1 N to 10 N; (iv) preparing, separately from the sodium silicate solution prepared in step (ii), a stable silica sol at an ambient temperature by adding a second part of the sodium silicate solution of step (i) to a part of the mineral acid solution provided in step (iii) under continuous agitation; (v) heating the sodium-ion-adjusted dilute sodium silicate solution prepared in step (ii) at an elevated temperature in the range of from 50° C. to 90° C.; (vi) neutralizing from 10 percent to 30 percent of the total alkali present in the sodium silicate solution of step (v) with a part of the dilute mineral acid solution provided in step (iii) over a time period of 5 to 20 minutes, under stirring, at an elevated temperature in the range of from 50° C. to 90° C.; (vii) interrupting the neutralization of the sodium silicate solution in step (vi) for a time in the range of from 5 minutes to 30 minutes while maintaining the elevated temperature; (viii) neutralizing the sodium silicate solution obtained in step (vii) with stable silica sol prepared in step (iv) over a time period of from 10 minutes to 30 minutes, under stirring; (ix) interrupting again the neutralization of the sodium silicate solution for a time period of from 3 minutes to 10 minutes; (x) adding a part of the dilute mineral acid solution provided in step (iii) to the above said reaction mixture of step (ix) over a time period of 5 to 30 minutes to adjust the pH of the reaction mixture to a value of from 3 to 5; (xi) aging the reaction mixture of step (x) for a time period of from 2 minutes to 10minutes; (xii) circulating continuously the reaction mixture through a centrifugal pump at a rate of from 15 cycles to 20 cycles per hour during steps (vi) to (xi); (xiii) separating solid silica from the reaction mixture by filtration, and by washing the resultant filter cake with water to remove adhering impurities; (xiv) drying the filter cake at a temperature in the range of from 90°C. to 110°C.; and (xv) pulverizing the solid silica to obtain finely divided silica powder.