Effects of maceral composition on pyrolytic behaviour of kerogens

Abstract

Optical microscopy, thermogravimetry and stepwise pyrolysis-gas chromatography were applied to three oil shale kerogens. Colorado kerogen, consisting mostly of alginite, gave a sharp d.t.g. peak, whereas Condor and Maoming kerogens, composed of alginite and vitrinite (~ 9:1) gave slightly broader peaks. Step-py-g.c. of all the kerogens gave many peaks of 1-alkene and n-alkane homologues. Condor and Maoming kerogens also gave several moderate g.c. peaks of phenolic compounds, which were hardly seen in the pyrograms of Colorado kerogen. The yields of the phenolic compounds were not strongly dependent on pyrolysis temperature, compared with alkenes and alkanes. The phenolic compounds were thought to be derived from vitrinite. This was confirmed by examining Ozasa vitrinite, for which step-py-g.c. gave large peaks of phenolic compounds similar to those from kerogens in terms of molecular weight distribution and generation profile. These results indicate that maceral composition is an important factor in the pyrolytic behaviour of kerogen.