Chromatographic evaluation of some selected polycyclic aromatic hydrocarbons of coal tars produced under different coking conditions and pitches derived from them

The volatile fractions of carbon disulfide extracts in tars and pitches have been studied by gas chromatography (GC), using the stationary phase OV-1701. Major polycyclic aromatic hydrocarbons (PAHs) in the fractions were selected as a basis for assessment of differences in the compositions of tars associated with their production. Several coal tars produced by wet charging carbonization in industrial- and semi-industrial-scale ovens with different mean flue heating temperatures were analyzed. The effects of preheating coal at about 200 degrees C prior to the coking process were also studied. From chromatographic data, ratios of different individual compounds or classes of compounds were calculated. They revealed that an increase in the carbonization temperature and coal preheating produced similar effects on tar and pitch composition, leading to a reduction in methyl-substituted PAHs, non-alternant PAH systems and highly reactive compounds such as acenaphthylene. A higher proportion of peri-condensed PAHs and PAHs with a higher degree of condensation were also observed. GC analysis provides an adequate method for estimating the degree of pyrolysis of tars in coke ovens and their thermal stability in pitch production.