Transformation mechanisms of organic S/N/O compounds during microwave pyrolysis of oil shale: A comparative research with conventional pyrolysis

Abstract

This study conducted experiments on shale oil production with less S/N/O compounds by microwave pyrolysis of oil shale (MW) compared with conventional pyrolysis (CON). Mass balances of S/N/O elements during MW and CON were performed. Organic S/N/O compounds in shale oils were identified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and their transformation mechanisms were investigated at a molecular level. Results indicate MW promoted S/N/O transform into chars and/or gases, reducing contents in shale oils by the maximum of 76.13, 13.22 and 27.86%, respectively. MW primarily facilitates rupture of CS and CN bonds and polymerization in S/N/O compounds. For S/N compounds with lower double band equivalents (DBEs), CS and CN bonds are readily to break producing H2S and NH3, while for those with higher DBEs, polymerization tends to occur. These reactions augmented the relative abundances (RAs) of S/N compounds with higher DBEs. For O2 species, however, side chains containing carboxyl group tend to fragment from aromatic rings, thus fatty acids (DBE = 1) present the highest RAs. Reaction mechanisms of S/N/O compounds during MW were proposed and discussed at a molecular lever, which would provide technical guidance for industrial applications.