Structural characterization of thermal bitumen extracted from Fushun oil shale semi-coke with ionic liquid/N-methyl pyrrolidone

Abstract

Thermal bitumen is an organic intermediate during the pyrolysis of oil shale kerogen. In this work, semi-cokes were prepared for obtaining thermal bitumen by pyrolyzing Fushun oil shale to 400–500 °C, followed by extraction with a mixture of an ionic liquid (1-butyl-3-methylimidazolium chloride) and a polar solvent (N-methyl pyrrolidone). The critical thermal bitumen with the highest yield of the 450 °C semi-coke extraction was carefully performed by gas chromatography–mass spectrometry, Fourier transform infrared spectrophotometry, liquid-state 13C nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The thermal bitumen was mainly composed of aliphatic structures, especially methylene chains. The dominant aliphatic hydrocarbons were between C13 and C27, and the alkanes and corresponding alkenes from C14 to C22 were continuously identified in pairs. A small quantity of benzenes and naphthalenes was identified as well as phenols, carboxylic acids, and nitrogen compounds. The oxygen functional groups were mainly carbon and oxygen double bonds, and the nitrogen and sulfur functional groups were characterized as pyrrole and thiophene. Ultimately, a structural formula (C370H570O29N4S) and its atomic distribution were proposed, based on the final analysis of experimental data.