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.

No abstract

Several chromatographic procedures were developed by the authors for the structural characterization and fractionation of pitches. Six coal tar pitches obtained by heat treatment under different conditions, together with a typical mesophase petroleum pitch, chosen for comparison, were studied following these procedures. The results gave an insight into the kind and extension of the chemical transformation occurring in pitch structure as a consequence of heat treatment. A good LC fractionation in compound classes (confirmed by FT-IR and HPLC analyses) of the toluene-soluble materials was achieved. The thermal behavior of the pitches was studied by thermogravimetric analysis and differential thermogravimetry, establishing a correlation between the softening point and the temperature of maximum weight loss rate. When toluene-soluble fractions are considered, HPLC and LC results indicate that the increasing heat treatment temperature gives rise to a decrease in the content of unsubstituted planar cata-condensed compounds, with a corresponding increase in the peri-condensed compounds concentration and a general increase in the condensation degree of polyaromatic structures. The distillation of the parent tar, followed to obtain the soft coal tar pitch CTSP, promotes an extensive removal of alkyl- and aryl-substituted aromatic compounds which are subsequently present in small quantities in all the studied pitches. Petroleum pitch PP consists of a high proportion of substituted cata-condensed compounds while coal tar pitch CTP-2, with similar SP and QI content, contains peri-condensed compounds and β-resins as its main components.

No abstract