Vacuum pyrolysis of maceral concentrates in a wire-mesh reactor

Abstract

The pyrolytic behaviour of maceral concentrates from three bituminous coals was investigated in a wire-mesh reactor under vacuum and at atmospheric pressure. A new set of traps, designed to overcome difficulties encountered in tar capture and recovery during vacuum pyrolysis, has been developed. Experiments reported were carried out at 1000 K s −1 to 700 °C with a 5 s hold; tar characterization was carried out by size exclusion chromatography, u.v. absorption and u.v. fluorescence spectroscopy. During pyrolysis experiments with whole coals, vitrinite, liptinite and inertinite concentrates, it was systematically found that about 5 wt% more gas was formed at atmospheric pressure than under vacuum. No major synergistic effects were observed between the petrographie components of coals during pyrolysis. Liptinite concentrate tars were found to have larger molecular mass distributions than tars from other maceral concentrates, and were found to undergo greater change from vacuum to atmospheric pressure. U.v. absorption and u.v. fluorescence spectra suggested that tars produced at atmospheric pressure were richer in aromatic content compared to vacuum tars. Liptinite concentrate tars appear to be more aliphatic/hydroaromatic in character and to have shown greater sensitivity to intraparticle secondary reactions. Spectra of tars from all three maceral concentrates show similar structural features suggesting that aromatic cluster size distributions of tars from different macerals may not be significantly different even though their aromaticities may differ.