Method for producing silicic acid with variable thickening

A process for production of silica having variable thickening, the process comprising reacting:

• a) a product stream I comprising at least one silicon compound selected from the group consisting of a vaporous silicon compound, a hydrolysable silicon compound, and an oxidizable silicon compound,
• b) a product stream II comprising oxygen, and
• c) a product stream III comprising a combustible gas,
• wherein the process comprises:
• importing product stream I into product stream II, or importing product stream II into product stream I, through a feed port in a first pipe piece A to create product stream IV, wherein the first pipe piece A comprises at least one static mixing element;
• importing product stream III in product stream IV, through a feed port in a second pipe piece B to create product stream V, wherein the second pipe piece B comprises at least one static mixing element;
• importing product stream V leaving the second pipe piece B into a reaction chamber, igniting the reaction chamber, and reacting the product stream V in a flame;
• and
• separating solids resulting from the ignition and the reaction.