This study presents the first combined application of 13C labeling and isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS) to analyze the thermochemical transformations of specific organic compounds within a complex heavy oil. Specifically, this technique was used to monitor the hydrocarbons produced during the carbonization of a fluid catalytic cracking decant oil (FCCDO). Structural GC/MS analysis of these products has previously shown that 4-methyldibenzothiophene, 13C-labeled at the methyl position (4-13MDBT), undergoes methylation to form a number of polymethyldibenzothiophenes and cleavage of its aryl-methyl bond to give dibenzothiophene (Energy Fuels 1997, 11, 623, 631). The irmGCMS analysis of these products shows that the 4-13MPBT is a source of 13C-enriched methyl that reacts with polyaromatic hydrocarbons (PAH) to produce a number of methylated PAHs. Precise measurement of 13C enrichment and concentration of specific compounds enables tracking of the labeled carbon within a complex mixture as a function of reaction time. There are large differences in apparent reactivities of mono- and dimethyl-substituted naphthalenes, phenanthrenes, and pyrenes. The differences in observed reactivities of methylnaphthalene, methylphenanthrene, and methylpyrene isomers are consistent with calculated free valence indices at specific positions. There is no significant 13C enrichment in unsubstituted PAH compounds, indicating that the labeled methyl group is not involved in producing GC-amenable unsubstituted PAH during early carbonization. This combined use of 13C-labeled reactants and irmGCMS analysis will have broad applications in oil processing and geochemical fields associated with the study of thermochemical transformations of organic compounds within complex mixtures.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology