SELECTIVE CONVERSION OF FUEL-BOUND NITROGEN TO N-2 WITH IRON NANOPARTICLES

The highlight of this review article is a novel method to remove fuel- bound nitrogen as N-2 during coal pyrolysis in an inert atmosphere. Wh en a Cl-free iron catalyst is precipitated on Australian brown coal fr om FeCl3 solution using Ca(OH)(2), N-2 yield increases with increasing pyrolysis temperature and reaches 50% at 900 degrees C, whereas it is < 5% without the iron. A low loading (1 wt% Fe) is sufficient for the remarkable formation of N-2, and the use of H-2 instead of inert He i s unnecessary. The iron catalyst decreases the partitioning to not onl y volatile nitrogen (tar, HCN, and NH3) but also char nitrogen. A smal ler catalytic effect of the precipitated iron is observed with bitumin ous coal. The iron catalyst after pyrolysis exists as fine particles w ith a smaller size of 20-30 nm for the brown coal char, Fe3C and graph itized carbon being also present. It is likely that N-2 originates mai nly from solid phase reactions involving the formation and subsequent decomposition of iron nitrides. In the pyrolysis of different coals at 1000 degrees C, N-2 yields for low-rank coals from China and Germany reach 50-60% despite the absence of catalyst. Demineralization with HC l washing removes mainly Fe and Ca elements from these coals and drast ically decreases N-2 yield with a corresponding increase in nitrogen r etention in the chars. The Ca ion-exchanged with the demineralized coa ls is inactive for N-2 formation. Iron nanoparticles, derived from Fe- containing minerals, catalyze predominantly solid phase reactions to e xtract N-2 from char and/or precursors.