ROLE OF IRON CATALYST IMPREGNATED BY SOLVENT SWELLING METHOD IN PYROLYTIC REMOVAL OF COAL NITROGEN

Organometallic iron precursors, ferrocene and ferric acetate, were impregnated into Illinois No. 6 (IL), Wyoming (WY), and Yallourn (YL) coals by solvent swelling technique in THF, ethanol, and a THF/ethanol binary solvent. Then iron-impregnated coals were pyrolyzed in a flow of helium at atmospheric pressure in a fixed bed and a thermobalance. Conversion of coal nitrogen to Na was 20, 38, and 30%, respectively, for original IL, WY, and YL coals. Iron formed from both precursors lowered the onset temperature of N-2 evolution by 20-100 degrees C. When ferrocene was impregnated in coals at a concentration of 1.7-1.8 wt % as Fe, nitrogen conversion was increased to 52, 71, and 68% for IL, WY, and YL coals, respectively. Ferric acetate impregnated into IL coal from THF/ethanol solution increased the nitrogen conversion much more than that from ethanol solution. The expansion of microporous coal structure by the swelling was essential for better dispersion of the catalyst precursor. The evolution of HCN as well as NH3 was effectively suppressed above 600 degrees C by the presence of iron but not influenced significantly by combinations of catalyst precursors and solvents. The increase in N-2 yield was compensated by the decrease in nitrogen emitted as HCN and NH3 and in tar and char. The increase in CO evolution from the iron-impregnated IL coal at 600-800 degrees C was explained by catalytic rearrangement of aromatic structure of char, accompanying the removal of nitrogen as N-2. In a range of 600-750 degrees C, the evolution of CO as well as N-2 from the other coals increased remarkably with a significant decrease in CO2 evolution, which was caused by iron-catalyzed CO2 gasification in char micropores.