THERMAL-BEHAVIOR OF EXTROGRAPHIC FRACTIONS OF COAL-TAR AND PETROLEUM PITCHES

Two coal tar pitches and a petroleum pitch were fractionated by extrog raphy on a preparative scale. The chemical composition of the fraction s 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 als o carbonized in a horizontal furnace, and the resulting cokes were cha racterized by optical microscopy. Exo- and endothermic effects shown b y the d.t.a. curves of extrographic fractions of the pitches were asso ciated with the physicochemical phenomena expected to occur during the pyrolysis of their respective constituents. It was found that the com position of a pitch and the reactivity of its constituents are reflect ed in the degree of overlap between the endothermic effect of volatili zation and the exothermicity of polymerization. The study of the optic al texture of the cokes in relation to the chemical and structural com position of the pyrolysed samples provided new evidence on the relatio ns between composition, reactivity and thermal behaviour of pitches. C opyright (C) 1997 Elsevier Science Ltd.