Comparison between reaction products obtained from the pyrolysis of marine and lacustrine kerogens

Abstract

The reactivity of kerogens from two different types of oil shales, marine Attrat oil shale from Jordan (type II kerogen, high sulfur) and lacustrine Colorado from USA (type I kerogen, low sulfur) has been studied. The kerogens were obtained using the NaOH/HCl demineralization method. The reaction products from the kerogens were compared with those from the raw shales. The reactivity of Attrat and Colorado kerogens was measured using sealed autoclaves at 355 and 390 °C for 1–5 h under N2 or H2 pressure. Attrat kerogen showed a higher conversion than Colorado kerogen, probably due to its high sulfur content. Except for Colorado at 390 °C under N2, kerogen was more reactive than the raw shale. The reactions under H2 produced higher oil yields for Attrat raw shale and kerogen when compared to their reactions under N2. The reactions of Colorado under H2 showed the opposite effect in most cases. The yields of CH2Cl2-solubles + water + hydrocarbon gas + sulphide gas increased with temperature whereas those of asphaltene and asphaltol decreased. CH2Cl2-solubles from both kerogens showed high atomic H/C ratios, with high sulphur content (Attrat) and nitrogen content (Colorado), as expected from the properties of the original kerogens. The proton nuclear magnetic resonance (1H NMR) indicated the highly aliphatic character of both CH2Cl2-solubles and, in contrast to what was observed for the raw oil shales, no significant change when H2 was substituted for N2. The aromaticity of CH2Cl2-solubles was higher for Attrat than Colorado (0.4 vs 0.3) as for the original kerogens, and the aromatic rings in both cases were heavily substituted. The gas chromatography-mass spectrometry (GC–MS) for both kerogen reaction products indicated highly aliphatic character; Attrat kerogen reaction products were distinguished by the presence of substituted thiophenes and benzothiophenes while these compounds could not be detected in Colorado kerogen reaction products. The marked differences between the reactions of the two kerogens did not appear to be due to effects of marine/lacustrine character, as such, but rather to the high S content of Attrat kerogen.