Reduction and carburization of metal oxides by methane-containing gas
This paper presents examination results of reduction and carburization of the oxides of iron, manganese, chromium, and titanium by CH4–H2–Ar gas mixture. The reactions were investigated in a laboratory fixed-bed reactor in temperature-programmed and isothermal- reduction experiments. The extents and kinetics of the reduction of metal oxides as a function of gas composition and temperature were determined by on-line, off-gas analysis using a mass spectrometer. Methane-containing gas with high carbon activity (above unity relative to graphite) provided strongly reducing conditions, in which metal oxides were reduced and carburized to metal carbides. Iron oxide was first reduced to metallic iron by hydrogen, and then metallic iron was carburized to cementite by methane. Manganese oxides were reduced to carbide Mn7C3; the product of reduction of chromium oxide was carbide Cr3C. Rutile was reduced to titanium oxycarbide in the following sequence: TiO2 3 Ti5O9 3 Ti4O7 3 Ti3O5 3 Ti2O3 3 TiOxCy. Reduction by methanecontaining gas occurs through adsorption and dissociation of methane with formation of adsorbed active carbon. Deposition of solid carbon retards the reduction.