Study on the aluminium chloride-modification for heavy fraction of light diesel oil using tandem mass spectrometry

Abstract

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.