Article révisé par les pairs
| Résumé : | The influence of iron oxide additions on coal pyrolysis has been studied by thermogravimetry and the analysis of the evolved gases. Liquid yields and tar composition were studied by complementary experiments on a larger scale. The presence of iron oxides reduces the primary-devolatilization rate of coal, between 300 and 600 °C. Tar and gaseous hydrocarbon yields decrease, but the tar composition does not change. Addition of magnetite, which is not reduced below 600 °C, results in a slight increase in hydrogen production at low temperature. However, at under 600 °C, Fe2O3 is reduced to Fe3O4, yielding a little CO2 and water. Towards the end of the primary devolatilization of coal, in the presence of iron oxide, the production of methane increases. In every case hematite has a greater influence than magnetite. The effects are smaller at low heating rates, and they occur with small additions of oxide, further additions having less influence. Iron oxides do not affect the primary devolatilization of lignite. With caking coals, the influence of rank is small. These observations are attributed to a superposition of three effects: 1. (1) the physical effect of oxide particles among coal particles, impeding the formation of the plastic state, 2. (2) the catalytic effect upon aromatization reactions of the metaplast, to form semi-coke, and upon secondary-formation reactions of methane, and 3. (3) the chemical effect of hematite reduction, preferentially using hydrogen required to form tar and gaseous hydrocarbons. The iron oxide structure, responsible for contact between the coal and oxide particles, is also important. © 1980. |
