Precipitated silica and process for its manufacture

Abstract

A precipitated silica characterised by the presence of specific acid sites on its surface and a process for its manufacture.

1 . Precipitated silica characterised by:
 an amount of at least one element M selected from the group consisting of B, Al, Ga and mixtures thereof in the range from 0.5 to 30.0 mol %;   an infrared absorption spectrum having at least one peak between 1538 and 1559 cm −1  and one peak between 1612 and 1635 cm −1 , said spectrum having been measured after chemisorption with pyridine to saturation followed by treatment under vacuum at 25° C., wherein the ratio (area under the peak between 1538 and 1559 cm −1 )/(area under the peak between 1612 and 1635 cm −1 ) is less than 0.80.   
     
     
         2 . The precipitated silica of  claim 1  wherein the area under the peak between 1538 and 1559 cm −1  is at least 0.02 cm −1 . 
     
     
         3 . The precipitated silica of  claim 1  wherein the area under the peak between 1612 and 1635 cm −1  is at least 0.03 cm −1 . 
     
     
         4 . The precipitated silica of  claim 1  wherein the at least one element M is selected from the group consisting of Al and Ga. 
     
     
         5 . The precipitated silica of  claim 1  wherein the amount of at least one element M is in the range from 0.7 to 25.0 mol %. 
     
     
         6 . The precipitated silica of  claim 1  characterized by a BET surface area SBET from 40 to 800 m 2 /g. 
     
     
         7 . A process for preparing the precipitated silica of  claim 1 , the process comprising the reaction of a silicate with an acid to produce a suspension of precipitated silica, said reaction comprising at least one step wherein either a silicate or at least one compound of element M is added to the reaction medium while the reaction medium is at a pH from 2.0 to 6.0, and wherein the at least one compound of element M is added to the reaction medium after at least 50% by weight of the total amount of silicate required for the reaction has been added to said reaction medium. 
     
     
         8 . The process of  claim 6 , said process comprising the steps of:
 (i) providing a starting solution having a pH equal to or greater than 7.0;   (ii) reducing the pH of the reaction medium to a value lower than 7.0 by either simultaneously adding a silicate and an acid or by adding an acid to said starting solution; and   (iii) simultaneously adding to the reaction medium a silicate and an acid, such that the pH of the reaction medium is maintained in the range from 2.0 to 6.0 to obtain a suspension of precipitated silica,   wherein at least one compound of element M is added to the reaction medium during step (ii) and/or (iii) with the proviso that such addition takes place after at least 50% by weight of the total amount of silicate required for the reaction has been added to the reaction medium.   
     
     
         9 . The process of  claim 6 , said process comprising the steps of:
 (i′) providing a starting solution having a pH equal to or greater than 7.0;   (ii′) reducing the pH of the reaction medium to a value lower than 7.0 by either simultaneously adding a silicate and an acid or by adding an acid to said starting solution; and   (iii′) simultaneously adding to the reaction medium an acid and at least one compound of element M, such that the pH of the reaction medium is maintained in the range from 2.0 to 6.0 to obtain a suspension of precipitated silica with the proviso that such addition takes place after at least 50% by weight of the total amount of silicate required for the reaction has been added to the reaction medium.   
     
     
         10 . The process of  claim 7  wherein, when M is B or Ga, the following additional steps are carried out after steps (iii) and (iii′):
 (iv) stopping the addition of the acid and raising the pH of the reaction medium to a value from 7.0 to 10.0; 
 (v) simultaneously adding an acid and a silicate to the reaction medium in such a manner that the pH of the reaction medium is between 7.5 and 9.5; and 
 (vi) stopping the addition of the silicate while continuing the addition of the acid to the reaction medium to reach a pH of the reaction medium of less than 6.0 to obtain a suspension of precipitated silica. 
 
     
     
         11 . A composition comprising the precipitated silica of  claim 1  and at least one polymer. 
     
     
         12 . The composition of  claim 10  wherein the at least one polymer is selected among the group of elastomers. 
     
     
         13 . An article comprising the composition of  claim 10 . 
     
     
         14 . The article of  claim 12  in the form of a footwear sole, floor covering, gas barrier, roller for cableways, seal for domestic electrical appliances, seal for liquid or gas pipes, braking system seal, pipe, sheathing, it cable, engine support, battery separator, conveyor belt, or transmission belt. 
     
     
         15 . A catalyst, catalyst support, thermal insulation material, resorcinol-formaldehyde/silica composite, absorbent for active materials, additive for toothpaste, concrete or paper comprising the precipitated silica of  claim 1 . 
     
     
         16 . The precipitated silica of  claim 5  wherein the amount of at least one element M is in the range from 0.8 to 25.0 mol %. 
     
     
         17 . The precipitated silica of  claim 6  characterized by a BET surface area SBET from 50 to 450 m 2 /g. 
     
     
         18 . The process of  claim 7 , wherein either the silicate or the at least one compound of element M is added to the reaction medium while the reaction medium is at a pH from 3.0 to 5.0.