Reduction of Manganese Oxides by Methane-containing Gas

Abstract

The paper presents results of reduction of pure manganese oxides by methane containing gas in nonisothermal and isothermal experiments and reduction mechanisms. The extent and rate of manganese oxide reduction were determined by on-line off-gas analysis using a mass-spectrometer in a fixed bed laboratory reactor in the temperature range 1 000-1 200°C at different gas compositions.Manganese oxides were reduced to carbide Mn 7 C 3 . High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15-50 (relative to graphite). The rate of reduction of manganese oxide increased with increasing temperature. Increasing methane content in the reducing gas to 10-20 vol% CH 4 favoured the reduction process. Increase in hydrogen partial pressure had a positive effect on the reduction rate. Addition of carbon monoxide to the reducing gas retarded the reduction process. The addition of Fe 3 O 4 to manganese oxide increased the rate of reduction.Reduction by methane-containing gas occurs through adsorption and cracking of methane with formation of active adsorbed carbon. Deposition of solid carbon retarded the reduction.

Carbothermal Reduction of Quartz in Methane–Hydrogen–Argon Gas Mixture

“…Our experimental study of direct reduction of quartz or amorphous silica powder by methane demonstrated that intermediate product SiO vapor escaped from the reaction zone as fume during reaction without conversion to SiC. This problem is not encountered in reduction of other metal oxides by methane as their intermediates are in the form of metals (Fe [17,18] ) or solid suboxides (Mn x O y [15] and Ti x O y [14] ) which are further converted to metal carbides by reacting with methane or deposited carbon. The gaseous SiO can be ''caught'' providing an intimate contact of quartz with solid carbon either by chemical vapor deposition from methane in silica particles before reduction [20] or by mechanical mixing of carbon and silica.…”

“…Solid carbon deposited on the sample surface by Reaction [15], hindering the further progress of reduction by blocking the particles' surface and preventing carbon supply for further reduction to the pellet's interior.…”

“…Increasing hydrogen content suppressed methane cracking and solid carbon deposition by Reaction [15]. Figure 10 presents the relationship between the extent of methane decomposition and the initial hydrogen content in the inlet gas at 1773 K (1500°C).…”

“…Intensive researches have been conducted in the production of various metal carbides using methane. Ostrovski and Zhang [13][14][15][16][17][18] investigated the reduction and carburization of the oxides of iron, manganese, chromium, and titanium by CH 4 -H 2 -Ar gas mixtures. 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.…”

“…MnO ! Mn 7 C 3 [15] ; and Rutile was reduced to titanium oxycarbide in the following sequence: [14] Lee et al [19] implemented a thermodynamic analysis of carbothermal formation of SiC and elemental Si.…”