Promoted catalysis of calcium on the hydrogasification reactivity of iron-loaded subbituminous coal

- Ca facilitated the dispersion of metallic Fe in coal char.
- Ca and Si formed Ca3SiO5 to promote the reduction of iron oxide to iron metal.
- Ca species existing as CaO(COO) could release CO2 which react with Fe3C.
- Fe-(O)-C triggered hydrogasification and maintained the high dispersion of Fe.

The calcium as a promoter in iron-catalyzed hydrogasification of sub-bituminous coal was studied to examine the catalytic activity of the Fe-Ca dual systems at H2 pressure 0.1-3.0 MPa, temperature 650-750 °C. Experimental results showed that the yields of light aromatic hydrocarbons (LAHs) and methane (synthetic natural gas, SNG) could be greatly improved at a given ratio of calcium-iron. Maximum yields of light aromatic hydrocarbons, 3.38 wt% (2.47 wt% of BTX and 0.34 wt% of naphthalene) were achieved using 5% Fe + 1% Ca dual catalysts at the catalyzed hydrogasification conditions of 750 °C and 1.0 Mpa. Analyses of coal chars were investigated to explain the promoted catalysis. The calcium promoted the reduction of iron oxide to active metallic iron, the increased dispersion of iron by calcium was found to result from the enhanced iron-calcium interaction, which was monitored through the carbon dissolved into iron to formed Fe3C. The rate of iron-catalyzed hydrogasification increased with time during the isothermal mode, the added calcium accelerated the catalytic activity increase and converted the oxygen, aromatic contents in oil and coal char to the formation of H2O, CO, CO2, BTX, PCXN and CH4.