In this study, a low-temperature coal tar pitch (CTP1) was subjected to carbonization in order to study the formation, growth, and development of mesophase achieved under different conditions. The results were compared to those obtained with a petroleum pitch (PP) and a conventional high-temperature coal tar pitch (CTP2). CTP1 was converted to mesophase at a considerably lower temperature, and also mesophase develops and coalesces at a markedly higher rate for this pitch. Volatile matter removal is a key factor in mesophase formation, but chemical composition also plays an important role, with substituted cata-condensed compounds constituting very reactive components in terms of anisotropic material development. More specifically, the oxygenated functional groups and aliphatic substituents facilitate the growth of mesophase. In particular, the high concentration of phenolic compounds present in CTP1 seems to contribute to the fast coalescence of mesophase spheres. The effect of several additives was also studied. Ferrocene was the most efficient in terms of mesophase formation, but simultaneously inhibiting coalescence. In contrast the use of argon pressure during carbonization promotes contact between mesophase spheres.
The purpose of this work was to study the formation of mesophase spherules from a
low-temperature coal tar pitch under carbonization conditions. For comparison, the carbonization
of a high-temperature coal tar pitch and a petroleum pitch were also considered. Different
operating conditions during the carbonization process were used in an attempt to cover different
degrees of mesophase formation and development for each pitch. The parent pitches and the
semicokes thus obtained were analyzed by elemental analysis, optical microscopy, and Fourier
transform infrared spectroscopy (FT-IR). More significantly, the samples were subjected to thermal
decomposition under well-controlled operating conditions from room temperature to 850 °C in a
thermogravimetric analyzer (TG). The use of a mass spectrometer linked to the TG (TG-MS)
provides additional data about the devolatilization process, yielding information about the
evolution of different volatile products and about possible chemical reactions occurring during
thermal decomposition. Thus an insight into the process of mesophase formation is obtained.
The results from FT-IR, elemental analysis, and the TG-MS tests were compared with the different
extents of mesophase formation, checked by optical microscopy. According to the results, several
stages can be distinguished as temperature increases in the carbonization process of the pitches.
In the low-temperature coal tar pitch, the devolatilization of light components, especially phenols,
accounts for the most significant weight loss. Moreover, cross-linking contributes greatly to the
formation and development of mesophase, resulting in the predominance of bulk mesophase in
a relatively short time in the case of the low-temperature coal tar pitch.
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