Process for hydrophobing pyrogenically produced silicon dioxide

Abstract From the Canadian patent

After separating the hydrogen halide pyrogenically produced silicon dioxide is mixed with nitrogen and fed into a cyclone. After separating the silicon dioxide from the gases which are returned to the cooling zone of the production apparatus, the silicone dioxide is mixed first with organo-halo silane and then with water vapour and nitrogen. The hydrophobing reaction is subsequently carried out in a conventional manner in a fluidized bed reactor. The waste gases from the reaction are returned to the cyclone.