Carbonization and liquid-crystal (mesophase) development. Part 3. Co-carbonization of aromatic and heterocyclic compounds containing oxygen, nitrogen and sulphur

A detailed investigation is reported of the effects upon size and shape of anisotropic mesophase structures in resultant semi-cokes of co-carbonizing eighteen oxygen-, nitrogen- or sulphur-containing compounds with fluorene, carbazole and acenaphthylene. Carbonizations were carried out under pressures of 130 to 320 MN m⁻² to a maximum heat-treatment temperature of 873 K, the mesophases being examined by optical and scanning electron microscopy. Additions of phthalimide, phthalic anhydride or pyromellitic dianhydride to fluorene and carbazole caused development of anisotropic carbon where none was formed on carbonization of the single compounds, or enhanced existing mesophase growth processes. Improvements in mesophase growth result in improved graphitizability of the semi-coke. Of the oxygen-containing compounds, the polycyclics with quinone groupings, or monocyclic molecules with several functional oxygen groupings, assist the growth of anisotropy. Phenol severely retards mesophase growth. Reasons are advanced which incorporate mechanisms of liquid-crystal formation. The implication for coal carbonization is that as the oxygen content in coals, on coalification, becomes increasingly attached to aromatic systems, then the oxygen in prime coking coals may actually enhance the growth of the mesophase during its carbonization. Nitrogen- and sulphur-containing compounds on co-carbonization with acenaphthylene at nitrogen or sulphur contents greater than 3% by weight may cause deterioration of mesophase growth. Such compounds do not significantly affect the carbonization of prime coking coals, but may contribute to the smallness of anisotropic structures in the carbons from coals of lower rank.