Role of iron catalyst in fate of fuel nitrogen during coal pyrolysis

The fate of fuel nitrogen during the pyrolysis of brown and bituminous coals at 900 degrees C, in the presence of iron precipitated from FeCl3 solution, has been studied with a fluidized bed reactor. The catalysts at 0.2-0.7 wt % Fe promote N-2 formation, whereas they lower nitrogen conversions to HCN, NH3, N-containing oil, tar, and char. The nitrogen distribution is not changed significantly by increasing iron loading. The effect of the iron on nitrogen distribution is larger with brown coal, the conversion to N-2 being approximate to 50 and approximate to 20% for brown and bituminous coals, respectively. The size of iron particles is smaller in brown coal chars, which appears to lead to a larger catalytic effect. Comparison of nitrogen mass balances in the presence and in the absence of iron shows that N-2 comes from not only volatile nitrogen but also char nitrogen. The X-ray diffraction measurements reveal the presence of graphitized carbon as well as cementite (Fe3C) in brown coal chars. These observations suggest that carbon atoms in the char substrate interact with fine particles of metallic iron and that interstitial iron nitrides formed in this process are decomposed to N-2.