Effects of iron on the soot formation during coal pyrolysis.

• Iron inhibits the formation of soot significantly in the process of coal pyrolysis. • After addition of iron, microstructure defects in soot derived from coal pyrolysis increase and the size of the graphite layers become smaller. • Iron may inhibit carbonyl formation and promote C–O formation during the process of soot formation. The addition of metal to fuel can effectively control the soot emission. However, there are few studies on the effect of metallic additive to coal on soot emissions. In this study, the effect of iron on the characteristics of coal-derived soot was analyzed. Soot particles were obtained at different temperatures from coal pyrolysis in a drop tube furnace without and with the addition of iron nitrate (Fe(NO 3) 3) into the coal, respectively. The microstructure and functional group information of soot derived from coal were obtained through Raman spectroscopy, infrared spectroscopy and XPS. The results showed that the yield of soot derived from coal pyrolysis with iron addition was reduced by 48–68% than that derived from coal pyrolysis without iron addition at different temperature. With the iron addition, the number of holes in the graphite layers in soot produced by coal pyrolysis was increased, while the valued of sp2/sp3 and the length of graphite layer were decreased. At the same time, the C–O and COO-functional groups in the soot increased, and the carbonyl content decreased. These phenomena indicated that the addition of iron can significantly inhibit the soot formation in the coal pyrolysis process, increase the defects of graphite layers in soot, inhibit the carbonyl formation, and promote the formation of C–O during the process of soot formation. [ABSTRACT FROM AUTHOR]