Ruthenium ion-catalyzed oxidation for petroleum molecule structural features: A review

Abstract

Ruthenium ion-catalyzed oxidation (RICO) is an oxidative degradation approach for the structural investigation of petroleum fractions. It is based on the selective oxidation and near quantitative removal of aromatic carbon from aromatic petroleum fractions, while leaving the structural integrity of aliphatic units intact. RICO method has played a highly useful role in the investigation of the molecular structures of heavy petroleum. It distinguishes alkyl groups attached to aromatic rings, alkyl bridges between aromatic rings, the nature of aromatic condensation, etc. The application of RICO to petroleum chemistry was promoted by Strausz and coworkers for the study of asphaltene and other high molecular weight petroleum fractions. Structural details on asphaltenes and their ramifications were revealed by the RICO-based studies, and a hypothetical molecular model was proposed for the petroleum asphaltenes. The structural information obtained from the model is valuable for understanding such complex molecular systems. Another application of the RICO technique in the petroleum industry is the characterization of biomarkers in heavy petroleum fractions and kerogen, which were connected to the condensed core structures by chemical bonds. Generally, only the oxidation of aromatic carbon to carbon dioxide and carbonyl functionalities in RICO is considered; however, other reactions may also take place. Since they occur parallel to the oxidation of aromatic carbon, misinterpretation of the relevant experimental results may result. Recent research based on ultrahigh-resolution mass spectrometry has provided new evidence for the side reactions, which leads to a more informative interpretation of the RICO results. This paper reviews the RICO-related studies on petroleum fractions. The interpretation of RICO experimental results is also discussed.