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The molecular distributions and constitutions of several A-240 petroleum and coal tar pitch fractions were investigated using field desorption mass spectrometry. The molecular profiles of all samples analysed were greatly extended and the maximum mass weight of CTP-BSHI approached 640 corresponding to 13 aromatic fused-rings, while that of A-240-BS approximated to 784 matched to 14 kata-condensed rings. The coal tar pitch samples were mainly composed of peri-condensed polyaromatics, with kata-condensed PAHs amounting to 1 4 of total sample. In contrast, A-240 petroleum pitch samples consisted almost totally of polyacenes (or their isomers) and polyaryl alkanes. The extremely different characteristics in the compoundtype distributions between these two pitches reflect the different features of high temperature gas-phase pyrolysis and medium temperature liquid-phase pyrolysis reactions.

Tandem mass spectrometry was used to follow the low temperature catalytic modification of the diesel oil heavy fraction in the presence of aluminium chloride. The molecular distribution from chemical ionization mass spectroscopy (c.i.m.s.) of raw feedstock ranges from 150 to 250, with an average molecular weight of 219 (v.p.o.). That of the finally modified pitch ranges from 200 to 800, mainly concentrated between 200 and 500 with v.p.o. molecular weight of 452. The m.s.-m.s. fragmentation analysis of three dominant, characteristic protonated parent ions m z 207, 373, 385, showed ethyl phenanthrenes (-anthracenes), dimers from phenanthrene (anthracene) and C 1 -phenanthrene with substantial naphthenic groups, dimers from C 1 -phenanthrenes and copolymers from hexahydropyrene with phenanthrene, chrysene with C 2 -naphthalene, etc., respectively, to be the main structural types of these parent mass numbers. This modified pitch material, with a characteristic low degree of condensation and extensive naphthenic structures proved to be suitable for transformation into mesophase pitch with high fluidity and a large domain-type anisotropic texture.