Thermal behaviour of extrographic fractions of coal tar and petroleum pitches

Two coal tar pitches and a petroleum pitch were fractionated by extrography on a preparative scale. The chemical composition of the fractions was determined by elemental analysis, FT-i.r., H-1 n.m.r. and solid-state C-13 n.m.r. spectroscopies and number-average molecular weight, (M) over bar(n), and their thermal behaviour was studied using thermal analysis techniques (t.g., d.t.g. and d.t.a.). The fractions were also carbonized in a horizontal furnace, and the resulting cokes were characterized by optical microscopy. Exo- and endothermic effects shown by the d.t.a. curves of extrographic fractions of the pitches were associated with the physicochemical phenomena expected to occur during the pyrolysis of their respective constituents. It was found that the composition of a pitch and the reactivity of its constituents are reflected in the degree of overlap between the endothermic effect of volatilization and the exothermicity of polymerization. The study of the optical texture of the cokes in relation to the chemical and structural composition of the pyrolysed samples provided new evidence on the relations between composition, reactivity and thermal behaviour of pitches. Copyright (C) 1997 Elsevier Science Ltd.