UV-FLUORESCENCE SPECTROSCOPY OF DEAL PYROLYSIS TARS

Changes in UV-fluorescence spectroscopic properties of coal pyrolysis tars as a function of coal rank, maceral composition, and pyrolysis conditions have been investigated. The effects of excited-state interactions (intramolecular energy transfer and excimer formation) on UV-fluorescence spectroscopic properties of pyrolysis tars have also been evaluated. Changes in UV-fluorescence spectroscopic properties with molecular mass have been studied by acquiring the spectra of successive SEC retention volume resolved fractions of the same tar sample. Fluorescence spectroscopic properties of coal pyrolysis tars have been found to correlate with the rank of the original coals; taken together with findings from FT-IR spectroscopy and size exclusion chromatography, these data show the increasing aromaticity of the tar samples with increasing coal rank. Synchronous spectra clearly show two characteristic peaks centred around 350 and 400 nm, the relative intensity of the first peak decreasing and that of the second peak increasing with increasing coal rank. The observed progressive increases in fluorescence intensity at longer wavelengths with increasing coal rank are interpreted as showing the presence of larger aromatic ring systems in increasing concentrations with increasing rank of the original coal samples, probably coupled with progressively shortened bridge structures connecting aromatic ring systems. Due to the observed changes in UV-fluorescence spectroscopic properties with molecular mass, the observed trends with the whole tar samples have also been verified using SEC retention volume resolved fractions. Tars from the pyrolysis of different maceral concentrates of the same coal have been observed to show similar spectral profiles, although fluorescence and absorption intensities have been observed to change with maceral composition and pyrolysis conditions.