STUDY OF THE REPRODUCIBILITY AND SELECTIVITY OF COAL-TAR PITCH FRACTIONATION BY EXTROGRAPHY ON ALUMINA

The potential of extrography on alumina as a fractionation and characterization technique of coal tar pitches has been evaluated in terms of reproducibility and selectivity of separations. Parameters controlling extrography were carefully selected, and standard conditions were adopted by two different laboratories in a reproducibility study. Results relating to mass balances of extrography, selectivity of separation, thermal behaviour of the separated fractions and coke characteristics were comparable for interlaboratory runs. Selectivity of the separations was followed by chemical gas chromatography-mass spectrometry (g.c.-m.s.), nuclear magnetic resonance (n.m.r.), Fourier transform infrared (FT-i.r.) spectroscopy, thin layer chromatography-FID (t.l.c.-FID) and thermal thermogravimetric (TGA) and differential thermal analysis (DTA)] characterizations of both fractions and subfractions collected. Their derived cokes were studied by optical microscopy to determine their respective degree of anisotropy to relate chemical structure, thermal reactivity and coke quality. Concerning the mechanism of extrographic elution, analytical data suggest an extractive mechanism for the first eluted fraction, and dominant chromatographic processes for the more polar fractions.