Separation and characterization of size-segregated fractions (soot and char) of carbonaceous particulate produced from coal pyrolysis

The aim of the present work is the structural characterization of the solid carbon produced during the early stages of coal pyrolysis in a drop tube furnace operated at 1300°C in different environment gases, namely N2 and CO2. Electron microscopy has shown that the carbonaceous particulate is a mixture of char particles and submicron particles/aggregates, here named soot. An ad hoc method based on the sedimentation of ethanol suspensions was used for separating these two fractions suitable for further structural characterization. The properties of soot and char have been investigated by applying several techniques as electron microscopy, laser granulometry, Raman and FT-IR spectroscopy. Results showed that these two fractions differ not only in their particle size. In particular the fine carbon particulate is less reactive and is mostly ash-free, suggesting that its formation occurs in the gas phase, while the coarse (char) fraction mainly derives from coal pyrolysis as presenting residues of inorganic matter contained in the parent coal.