Correlation of pyrolysis-gas chromatography mass spectra and nuclear magnetic resonance spectra of pitch fractions separated by planar chromatography

A coal tar pitch from the high temperature coking of coal has been fractionated by planar chromatography into fractions immobile in pyridine, mobile in pyridine but not mobile in acetonitrile, and mobile in both solvents. Fractions have been examined by pyrolysis-gas chromatography/mass spectrometry at 770 and 1300 °C, and by nuclear magnetic resonance (NMR) methods (1H in solution and 13C (CPMAS TOSS) in the solid state). The fraction mobile in both solvents resembled the whole pitch in that the pyrolysis products were all polycyclic aromatics. The fraction mobile only in pyridine and the immobile fraction both gave alkene fragments as the most abundant pyrolysis products with polycyclic aromatics of low intensity only. The pyridine mobile and immobile fractions were shown by size exclusion chromatography with ultraviolet (UV) absorbance detection and by UV fluorescence spectroscopy to consist of large aromatic clusters and of large molecules. It is likely that the large aromatic clusters did not pyrolyse into fragments able to pass through the GC column. NMR methods confirmed the apparent trend of increasing aliphatic content with increasing immobility in thin layer chromatography.