Thermal Cracking of Substituted Cholestane-Benzoquinoline Asphaltene Model Compounds

Six asphaltene model compounds incorporating the biomarker structure of 5 alpha-cholestane, covalently fused to a range of differentially substituted benzoquinoline groups, were subjected to thermal cracking. Thermogravimetric analysis of the six compounds showed similar cracking kinetics and yields of solid residue (coke), with the heaviest compound, bearing a pyrenyl substituent, forming the largest amount of residue. Analysis of the products formed from thermal cracking of three such model compounds in a stainless steel microreactor showed mainly dehydrogenation of the saturated hydrocarbon rings, along with some peripheral demethylation, and steroid side-chain fragmentation, with no significant ring opening or release of cyclic substructures from the steroid moiety. Some loss of the aromatic substituents appended to the benzoquinoline moiety was also detected. Methylated products and dimers of the parent compounds were formed by addition reactions, which participated in further cracking and addition reactions as the conversion increased.