Comparison of solvent-soluble fractions of a petroleum residue and three coal tars by size exclusion chromatography (SEC), UV-fluorescence (UV-F) and mass spectrometry.

A petroleum atmospheric pressure distillate residue and three tars derived from coals using different severities of thermal treatment (a high temperature coal tar pitch, a coal liquefaction extract and a low temperature tar) have been fractionated using column chromatography on silica and seven solvent elutions. The fractions from the four extractions have been compared using SEC in 1-methyl-2- pyrrolidinone (NMP) as eluent and by synchronous UV-fluorescence (UV-F). Fractionation solvents were pentane (2 x 50 mL), toluene (100 mL), acetonitrile (100 mL), pyridine (100 mL), NMP (100 mL) and water (100 mL) using 1g of each sample. The two pentane-soluble fractions of 50 ml each from each sample eluted different components, with the second aliquot containing larger size aromatics than the first; the toluene-soluble fractions were of larger size by SEC, than the pentane soluble fractions. The toluene-soluble fraction from Petrox was of larger size than those from coal tars, but the three coal tars showed significant differences, indicating that temperature of pyrolysis had a significant effect on the molecular size. Synchronous UV-F spectra of the fractions in solution in NMP showed significant differences between the petroleum residue and the coal tars. The toluene solubles of petroleum residues and coal tars have molecular sizes by SEC, and aromatic chromophores by UV-F, that depend in part on the thermal treatment experienced in the formation of the tar or liquid. Coal tars are generally prepared using higher pyrolysis temperatures than those envisaged in the generation of petroleum crudes from kerogen. Fractions soluble in toluene approximate to asphaltenes, but it is clear that there are fractions dissolved from coal tars and Petrox residue that require more polar solvents than toluene.