Structural features of large molecular mass material in coal-derived liquids: catalytic hydrocracking of the pyridine-insoluble fraction of a coal-tar pitch
V. Begon et al., Structural features of large molecular mass material in coal-derived liquids: catalytic hydrocracking of the pyridine-insoluble fraction of a coal-tar pitch, EUR J MASS, 6(1), 2000, pp. 39-48
The pyridine-insoluble fraction of a coal-tar pitch has been catalytically
hydrocracked, The starting sample contained no material that could be obser
ved by gas chromatography/mass spectrometry (GC/MS) or by heated-probe mass
spectrometry, The aim of the study was to generate structural information
on this narrow cut of large-molecular-mass material, which consisted mainly
of compounds boiling above 450 degreesC, A much broader boiling-point dist
ribution was found for hydrocracked products; evidence from all analytical
techniques used (size-exclusion chromatography, W-fluorescence spectroscopy
and heated-probe mass spectrometry) indicated a significant reduction of t
he molecular mass range. A wide variety of aromatic groups was identified i
n hydrocracked products by heated-probe mass spectrometry, ranging from phe
nanthrene (m/z 178) to beyond dibenzocoronene (m/z 400), Ions corresponding
to alkyl (m/z 43, 57, 71 and 85) and alkenyl groups (m/z 41, 55, 69 and 83
) were detected. The results reflect the ability of the hydrocracking proce
ss to cleave bonds within large pitch molecules, releasing the structural u
nits which form the molecules. The structure of the original pyridine-insol
uble material may thus be seen as a series of aromatic groups linked by sho
rt bridges or small groups, but with some longer aliphatic bridges (C-12 an
d C-17) as shown by pyrolysis-GC/MS, Clearly, some molecular species were r
educed in mass but still lay above the range of detection by heated-probe m
ass spectrometry and could not be identified. Although the extent to which
large polycyclic aromatic entities themselves have been cracked (or otherwi
se reduced to smaller polycyclic aromatic groups) cannot be quantitatively
discerned from the present data, the hydrocracking of isolated fractions of
intractable coal-derived material appears to offer a useful method for pro
bing their structural features.