Structural features of Boscan and Duri asphaltenes

The molecular structural units of Boscan and Duri asphaltenes have been inv estigated in ruthenium-ion-catalyzed oxidation (RICO) and pyrolysis. From t he RICO reactions, homologous series of n-alkanoic acids (C-1-C-31), repres enting aromatic-attached n-alkyl side chains, alpha,omega-di-n- alkanoic ac ids (C-4-C-26), representing polymethylene bridges connecting two aromatic units, and benzenecarboxylic acids, indicating the major modes of aromatic condensations in the asphaltene molecules and the minor role of pericondens ed aromatic structures in them, were detected and measured. The RICO reacti on also yielded a nondistillable oxidized residue. Pyrolysis of this materi al after methylation yielded a homologous series of n-alkanes and n-alk-1-e nes, n-alkanoic and n-alkenoic acid methyl esters, and free n-alkanoic acid s with strong even-to-odd carbon preference. These products prove the prese nce of naphthenic-attached n-alkyl side chains and bridges, polymethylene b ridges connecting aromatic to naphthenic systems, and n-alkanoic acid ester /n-alkanol ether side chains attached to naphthenic carbons in the asphalte ne. Among the pyrolysis products of the whole asphaltene identified were ho mologous series of alpha- and alpha,alpha-n-alkyl-substituted thiolanes and thianes, a series of dicyclic terpenoid sulfides, along with a homologous series of 1-n-alkyldibenzothiophenes. In general, the nature of the pro duc ts identified were the same as those found in the asphaltenes from Alberta tar sand, carbonate bitumens, heavy oils, and some immature oils from China , but their distributions showed some variance, reflecting differences in b iotic source materials, source rocks, depositional environment, and diagene tic and thermal history.