Asphaltene Reaction Pathways. 1. Thermolysis

Petroleum asphaltenes were pyrolyzed at temperatures ranging from 350 to 565 °C for times from 5 to 150 min in batch tubing bomb reactors. Gas, maltene, coke, and unreacted asphaltene product fractions were recovered by using a solvent extraction sequence and were subsequently analyzed by GC and GC/MS. The variation of these products' yields with time and temperature provided insight to asphaltene structure, thermal reaction pathways, and processing schemes. Primary pyrolysis products included light heteroatomic and hydrocarbon gases, alkanes, cycloalkanes, and single-ring aromatics, from which the presence of corresponding moieties in the asphaltene was inferred. The product fractions’ temporal variations were consistent with an asphaltene structure containing a hydrogen-deficient, condensed aromatic core. These temporal variations also allowed discernment of primary and secondary thermal reaction pathways. The primary reaction of the asphaltene to each of its aromatic core and maltene andjgas fractions was followed by secondary degradation of these primary products to lighter compounds. These results suggest that catalyst deactivation during the hydroprocessing of heavy oils can be partially attributed to the precipitation and deposition of asphaltene and its aromatic core.