Glycoxy silanes as a source of silica and silicate precipitates

Abstract

The present invention discloses glycoxy silanes as a source of silica and silica precipitated by advantageous chemical reactions preferably beginning with biogenic silica. Alkoxy C—O—S 1 are hydrolyzed in a controlled fashion to nucleate formation of nanoparticles of silica. The growth rate of the particles is controlled by various parameters such that particles of known sizes, size distributions, specific surface areas and pore sizes and size distributions are recovered.

We claim: 
     
         1 . A method to precipitate silica comprising:
 neutralizing an amount of base in a solution comprising a silicon alkoxide containing 10-40 wt % dissolved silica, wherein alkoxy groups are selected from the group consisting of 1,2; 1,3; 1,4 diols; and triols; and polyols and mixtures thereof; hydrolyzing alkoxy C—O—Si bonds;   recovering precipitated silica by filtration; and   recycling recovered filtrate into a dissolution process, wherein silica is dissolved in a base to produce water soluble alkoxysilanes.   
     
     
         2 . The method of  claim 1 , wherein water is added to reduce pH. 
     
     
         3 . The method of  claim 1 , further comprising the step of controlling the pH of the solution to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof. 
     
     
         4 . The method of  claim 1 , wherein the neutralizing step comprises adding water and a sufficient amount of acid or CO 2  gas to lower the pH below about 8 to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof. 
     
     
         5 . The method of  claim 1 , wherein the neutralizing step comprises adding a sufficient amount of acid to lower the pH below 5 and adding a second base to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof. 
     
     
         6 . The method of  claim 5 , wherein the second base is ammonium hydroxide or an ammonium salt and the precipitated silica is a crystalline solid structure. 
     
     
         7 . The method of  claim 1 , wherein the neutralizing step comprises adding a sufficient amount of acid to lower the pH below 8 and adding a long chain alkyl ammonium salt and the precipitated silica is a crystalline solid structure. 
     
     
         8 . The method of  claim 1 , wherein neutralizing the step of lowering the pH comprises adding a sufficient amount of acid to lower the pH below 5 and adding a second base comprising a short chain alkyl ammonium salt selected from the group consisting of (HOCH 2 CH 2 )N(CH 3 ) 3 Cl; N(CH 3 ) 4 Cl; (HOCH 2 CH 2 )N(CH 3 ) 3 OH; N(CH 3 ) 4 OH; and combinations thereof to yield (R 4 N)(OSiO 1.5 ) 8    
     
     
         9 . The method of  claim 1 , wherein the 1, 2 diol is ethylene glycol, and the 1,3 diol is propylene glycol or glycerol and combinations thereof 
     
     
         10 . The method of  claim 1 , wherein the silicon alkoxide contains approximately 20-35 wt % dissolved silica. 
     
     
         11 . The method of  claim 1 , wherein the recovering step is preformed at temperatures of −20 to 180 o C. 
     
     
         12 . The method of  claim 1 , further comprising the steps of acid washing and drying the precipitated silica to produce silica with specific surface areas in excess of 400 m 2 /g and pore volumes of 0.5 to 1.5 cc/g. 
     
     
         13 . The method of  claim 1 , wherein the precipitated silica is acid washed and dried to produce silica with purities ranging from 99% to 99.9999%. 
     
     
         14 . The method of  claim 1  wherein the precipitated silica is acid washed and dried to produce silica with water contents of 0.1-10 wt %. 
     
     
         15 . The method of  claim 1  further comprising the step of recycling a filtrate to recover the diols, triols or polyols.