Vorrichtung zur Durchfuehrung von Gasphasenreaktionen

摘要

In a gas phase reaction forming a normally solid product at least one reactant gas is pre-heated to 250-800 DEG C. and subsequently heated before or during the reaction to 800-2000 DEG C. by an electric discharge running at 1-10 kv., any other reactant gas(es) being introduced cold or up to 800 DEG C., the gases being reacted in a primary reaction vessel of circular cross-section into which one hot gas is introduced tangentially to maintain inert spheres in motion to keep the vessel wall free of solid product, the reaction being completed in a secondary reaction chamber and the product being extracted from the cooled effluent gases. Oxides, nitrides, carbides, borides, sulphides, silicides and halides are prepared, particularly oxides of Ti, Si, Al, Fe as fine powders. In examples TiCl4 and air or oxygen react to form TiO2; SiCl4 is hydrolysed using steam to form SiO2; TiCl4 is reduced to TiCl3 using hydrogen. Mixtures, e.g. TiCl4 and AlCl3 or SiCl4 may be reacted with oxygen to form TiO2 particles coated with Al2O3 or SiO2. Preheating.-Reactants are evaporated and heated, e.g. to 250-800 DEG C. electrically or using chemical fuels. Superheating.-The electric discharge furnace may be combined with the primary reaction chamber (Fig. 8, not shown) or one or more gases may pass through separate discharge furnaces before reaching the chamber. The furnace runs at 1-10 kv. A.C. or rectified A.C., the voltage being applied between coaxial electrodes 3, 4 (Fig. 1), or two rod electrodes spaced apart, or electrodes (33), (36) (Fig. 8). Electrodes may be silicon carbide, molybdenum silicide, zirconium silicide, graphite cermets based on Cr-Al2O or Ni-ThO2, or nickel or steel may be used if cooled. A central electrode may be hollow, and inert gas may flow over it and down its central hole. An electrode may be rotated mechanically or by a rotary magnetic field. Halides K, Rb, Cs or Ba, hydrocarbons or nitrogen oxides may be added to the reactant gas to increase its conductivity, and gas is directed tangentially into the discharge (Figs. 1, 8). Primary reaction chamber.-In Fig. 1, one reactant passes through discharge furnace 1, 3, 4 and enters reactor chamber 6 tangentially, the other enters through 7. The conical shape of chamber 6 creates a vortex which causes rapid mixing and keeps inert spheres moving to prevent deposition on the walls. In Fig. 5 (not shown) chambers (21), (24) have annular compartments (20), (23) which deliver gas tangentially (details, Fig. 6, not shown). In use, for example, TiCl4 enters tangentially through (20) and 3 to 20% of necessary oxygen through (18) or (19). Seed crystals of TiO2 are formed and the turbulent mixture enters chamber (24) where the rest of the oxygen is added tangentially. Inert spheres are added through (18) or (19). In Fig. 8 the preheated gases enter tangentially from compartment (34) and at (33), (38) or (39), and a discharge between electrodes (33), (36) superheats them. Inert spheres may enter through hollow electrode (33) or at (38) or (39). The annular compartments used to deliver gases tangentially (Fig. 6, not shown) may be divided to deliver two gases through alternate apertures into a reaction chamber. Figs. 3, 4, 7 (not shown) illustrate other primary reaction chambers. The chambers are made of corundum, sintered magnesia, ZrO2, ThO2, SiC, BeO. The spheres are of 0.5 to 10 mm. diameter and may be Al2O3, SiO2, TiO2, ZrO2, MnO2, BeO, ZrSiO4, MgO, SiC, Si3N4, TiC, TiB2, ZrB2, MoSi2 or mixtures. Secondary reaction chamber &c.-The secondary reaction chamber in all cases is a well-insulated tube 9 (25), (37) (Figs. 1, 5, 8). At its far end, the reacted gas mixture is cooled by tangentially injecting cooled waste gas, water, organic liquids, or liquefied CO2, C2l, SO2, H2S or NH3 which may be one of the waste gases of the process. The solid product is recovered by passing the cooled gases through a cyclone separator or bag filter.