Patent ID: 6932953
Filing Date: 2005-08-23
Classification: C01B,C01P

Abstract:
1. A method for preparing particulate silica, comprising the step of feeding a gas mixture of at least one organohalosilane gas of the formula: R 4-n SiX n wherein R is hydrogen, methyl, ethyl or phenyl, X is a halogen atom, n is an integer of 1 to 3, with the proviso that n=3 when R is phenyl, a flammable gas capable of generating water vapor when burned, and a free oxygen-containing gas to a reaction chamber through a burner, whereby the organohalosilane is subjected to flame hydrolysis according to the scheme (I): wherein R, X and n are as defined above, and then to oxidation reaction according to the scheme (II): wherein C i H j is a general form of R 4-n so that i varies in the range of 0 to 6 and j varies in the range of 1 to 15 as R is hydrogen, methyl, ethyl or phenyl, n is as defined above, with the proviso that n=3 when R is phenyl, thereby forming particulate silica, having a specific surface area of 205 to 400 m 2 /g and a logarithmic standard deviation of primary particle diameter of up to 0.5 wherein the amount of said flammable gas fed is ½ to 3 mol per mol of said organohalosilane and such that the amount of water vapor resulting from combustion of said flammable gas is 1 to 2 times the stoichiometric amount in scheme (I), said burner has a plurality of concentric tubes including a center tube, having an outlet open to the reaction chamber, said gas mixture is fed to the center tube of said burner such that it may have a linear velocity at the outlet of the center tube of 50 to 120 m/sec, calculated in the standard state, and said flammable gas or said free oxygen-containing gas is fed to each outer tube arranged concentrically around the center tube of the burner.