Structural Transformations of Heavy Oil Asphaltenes in the Course of Heat Treatment: Fid-Bau Portal

Structural Transformations of Heavy Oil Asphaltenes in the Course of Heat Treatment

Cheshkova, T. V. / Grinko, A. A. / Min, R. S. / Sagachenko, T. A.

The composition of fragments linked by ester, ether, and sulfide bridges in heavy oil asphaltenes and in asphaltene components recovered from liquid products of their conversion at 300 and 450°C was studied by methods of selective chemical degradation and gas chromatography–mass spectrometry. The composition of “bound” fragments in molecules of secondary asphaltenes differs from that of products formed by cleavage of bridging bonds in molecules of the initial asphaltene samples and depends on the thermolysis temperature. At the initial thermolysis temperature, the mainly degrading fragments are those bound in the initial sample through the least thermally stable ester functional groups. An increase in the cracking temperature leads to the decomposition of bridges that link with each other structural fragments of macromolecules and separate aromatic clusters of the naphthene–aromatic system. Such bridges involve more thermally stable ether functional groups and С–S bonds in saturated and aromatic rings. The specific features of the distribution of “bound” fragments in the structure of the products of thermal degradation of the initial asphaltenes indicate that the asphaltene components of heavy oils contain molecules differing in the nature and position of sulfide, ether, and ester bridging bonds. The identified ether/ester-bound high-molecular-mass n-alkanes not only are covalently bound fragments but can also be occluded compounds that are released upon degradation of aromatic cores of asphaltene aggregates.