Characterization of organic nitrogen and sulfur in the oil shale kerogens

- All kerogens contain five forms of organic nitrogen and four forms of organic sulfur.
- The conjugated structure makes the relative amount of pyrrolic nitrogen remain stable in the metamorphism.
- With increasing amount of aromatic carbon, the relative amount of aromatic sulfur increases significantly.

Organic nitrogen and sulfur species along with carbon structural features in the five different oil shale kerogens were characterized by solid-state 13C NMR, XPS, and XRD techniques. Results indicate all the five kerogens contain aliphatic carbons in large amounts, aromatic carbons and small quantities of carbonyl and carboxyl carbons. Increased metamorphism results in increase in the number of aromatic carbons and corresponding decrease in that of aliphatic carbons. All kerogens contain five forms of organic nitrogen: pyridinic nitrogen, amine nitrogen, pyrrolic nitrogen, quaternary nitrogen, and nitrogen oxides. Relative amount of pyrrolic nitrogen is the highest and the majority of organic nitrogen exists as pyrrolic and quaternary nitrogens in comparable relative abundances, both accounting for > 70%. With increase in the number of aromatic carbon, the relative number of pyridinic nitrogen increases and that of amine nitrogen decreases. Forms of organic sulfur include aliphatic sulfur, aromatic sulfur, sulfoxide, and sulfone in all the kerogens. A small amount of inorganic pyrite sulfur is also present. Most of the organic sulfur (> 70%) exists as aromatic sulfur and sulfone. With increasing amount of aromatic carbon, the relative amount of aromatic sulfur increases significantly, whereas that of aliphatic sulfur decreases.