Thermoanalysis of the combined Fe3O4-reduction and CH4-reforming processes

The chemical equilibrium composition of the system Fe₃O₄ + 4CH₄, at 1300 K and 1 atm consists of solid Fe and a 2:1 gas mixture of H₂ and CO. Thermogravimetric (TG) analysis combined with gas Chromatographic measurements was conducted on the reduction of Fe₃O₄ (powder, 2-µm mean particle size) with 2.3, 5, 10, and 20 pct CH₄ in Ar, at 1273, 1373, 1473, and 1573 K. The reduction proceeded in two stages, from Fe₃O_{4 to FeO, and finally to Fe. CR}, conversion and H₂ yield increased with temperature, while the overall reaction rate increased with temperature and CH4 concentration. C (gr) deposition, due to the cracking of CR,, was observed. By applying a topochemical model for spherical particles of unchanging size, the reaction mechanism was found to be mostly controlled by gas boundary layer diffusion. The apparent activation energy reached a maximum at 30 pct reduction extent and decreased monotonically until completion. When compared with the results using instead either H₂ or CO as reducing gas, the reduction achieved completion faster using CH₄, at temperatures above 1373 K.