Separation and characterization of the isotropic phase and co-existing mesophase in thermally treated coal-tar pitches

The isotropic and anisotropic phases which co-exist in thermally treated coal-tar pitches (10-65 vol.% mesophase) were separated by pitch filtration. Optical microscopy showed that the filtrates were 100% isotropic, while the filtration residues had mesophase contents between 75 and 87 vol.%. The values of the characteristic parameters of the thermally treated pitches calculated from those of the fractions were in close agreement with the experimental values, indicating that the phases did not alter during the separation process. Comparison of the properties of the fractions showed that the anisotropic phases had a higher degree of polymerization than the isotropic phases, as reflected by the higher C/H atomic ratio, toluene and N-methyl-2-pyrrolidone insoluble content and carbon yield. Moreover, the effects of thermal treatment on the evolution of each phase were also studied. An increase in the degree of polymerization was observed in both phases. (C) 2000 Elsevier Science Ltd. All rights reserved.