MOLECULAR-STRUCTURE OF ATHABASCA ASPHALTENE - SULFIDE, ETHER, AND ESTER LINKAGES

Athabasca n-C-5-asphaltene was fractionated into occluded maltene, low and high molar mass (LMA, HMA) asphaltene, and the latter fractions w ere subjected to Ni2B reduction to cleave the sulfide C-S bonds, basic hydrolysis to cleave the ester C-O bonds, and BBr3 treatment to cleav e the ether C-O bonds. Ni2B reduction of asphaltenes yielded 5-18% n-p entane solubles, which were separated into saturates, aromatics, and p olars, and the saturates were analyzed for biomarkers. The residual as phaltene underwent 40% desulfurization and a greater than 4-fold drop in the MW of HMA but no change in the MW of LMA. The decrease in the M W is attributed to sulfide-bound core segments in the structure of the asphaltene: [core]-S-[core]-S-[core]-S-[core] + Ni2B --> 4[core] + 3H (2)S. This is an important structural feature of Athabasca asphaltene and is responsible for its upgradability without excessive coke format ion. The biomarkers of the asphaltene fractions were also characterist ically different with regard to maturity status and composition. Both fractions yielded n-alkanes, cheilanthanes, regular steranes, hopanes, and gammacerane, and the LMA also contained dicyclic terpanes and C-2 1-C-25 steranes. Noteworthy was the absence of diasteranes, which are the only steranes in the maltene. In terms of the 20S/(S + R) steranes and 22S/(S + R) hopanes parameters the maturity varies as maltene > L MA > HMA. This difference is a manifestation of the thermocatalytic na ture of the maturation process and the protection of the macromolecula r nature of the asphaltene against contact with external reagents. Ni2 B reduction indicates that (1) the n-alkane products arise from n-alky l substituted thiolane/thiane and thiophene and (2) C-27-C-30 steranes are attached to the asphaltene by one S atom, and the C-21-C-25 stera nes and terpanes by two S atoms. Basic and BBr3 hydrolyses of HMA show ed that both ester and ether linkages of n-acids and n-alcohols are pr esent and that the esters are of recent origin, whereas the ethers wer e derived from the original biotic source material of the bitumen.