COMPOUND-SPECIFIC ISOTOPE ANALYSES OF PRODUCTS FROM CARBONIZATION OF A FLUID CATALYTIC CRACKING DECANT OIL DOPED WITH C-13-ENRICHED 4-METHYLDIBENZOTHIOPHENE

This study presents the first combined application of C-13 labeling an d isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGC MS) 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 analy sis of these products has previously shown that 4-methyldibenzothiophe ne, C-13-labeled at the methyl position (4-(MDBT)-M-13), undergo es me thylation 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 -(MDBT)-M-13 is a source of C-13-enriched methyl that reacts with poly aromatic hydrocarbons (PAH) to produce a number of methylated PAHs. Pr ecise measurement of C-13 enrichment and concentration of specific com pounds enables tracking of the labeled carbon within a complex mixture as a function of reaction time. There are large differences in appare nt reactivities of mono- and dimethyl-substituted naphthalenes, phenan threnes, and pyrenes. The differences in observed reactivities of meth ylnaphthalene, methylphenanthrene, and methylpyrene isomers are consis tent with calculated free valence indices at specific positions. There is no significant C-13 enrichment in unsubstituted PAH compounds, ind icating that the labeled methyl group is not involved in producing GC- amenable unsubstituted PAH during early carbonization. This combined u se of C-13-labeled reactants and irmGCMS analysis will have broad appl ications in oil processing and geochemical fields associated with the study of thermochemical transformations of organic compounds within co mplex mixtures.