SEMIQUANTITATIVE GAS-CHROMATOGRAPHIC ANALYSIS OF THE VOLATILE FRACTION IN SEVERAL EXTRACTS OBTAINED BY TREATMENT OF COAL-TAR PITCHES WITH DIFFERENT ORGANIC-SOLVENTS

The solubility of four coal tar pitches in several organic solvents an d the semiquantitative gas chromatographic analysis of the correspondi ng volatile fraction extracts are discussed. Close relationships betwe en the extraction yield and the chromatographic material concentration of the several extracts studied are found. These correlations show th at the increase in extraction ability from one solvent to another is b asically due to the solvent's ability to extract unchromatographed com pounds of high molecular weight. In general, hexane (pentane) and meth anol extract chromatographic fractions have a smaller concentration of compounds of high molecular weight. No solvent selectivity towards po lycyclic aromatic hydrocarbons, oxygenated compounds and thiophene der ivatives is found. Nevertheless, methanol shows greater tendency to ex tract pyrrole benzoderivatives than other groups of compounds, but the extractive ability of methanol towards this group of compounds is not the highest. It is observed that solvents with medium extractive abil ity are able to extract the same amount of chromatographed compounds p resent in a pitch as solvents with high effectiveness. Furthermore, a comparison between semiquantification by means of gas chromatography a nd infrared spectroscopy is made in order to test the scope of the vol atile fraction approach in pitch characterization. This comparison sho ws that the proportion of polycyclic aromatic hydrocarbons in chromato graphic and non-chromatographic fractions is fairly close.