The chemical structure and thermal evolution of oil Sands bitumen: Experimental and molecular simulation study

Abstract

In this study, the chemical structural units of two Indonesian oil sands bitumen (OSB) samples were experimentally characterized by advanced techniques. The results show that the chemical structure of OSB samples was dominated by aliphatic structures, with aliphatic carbon ratios of 0.54 and 0.58, respectively. The aromatic carbon structure exhibits a high degree of condensation, but a small number of rings. The structures with the most oxygen-containing functional groups consist of hydroxyl and aliphatic ethers. The sulfur-containing functional groups mainly consist of aliphatic sulfur, followed by aromatic sulfur. By studying the thermal evolution pattern of OSB functional groups at different temperatures, it was found that aliphatic structures form a large number of olefins and alkanes during pyrolysis. In contrast, aromatic structures undergo condensation reactions to form highly polymeric structures that are more difficult to decompose. Moreover, aliphatic sulfur is the main sulfur-containing functional group. It exhibits poor thermal stability and gets easily reduced during pyrolysis, which is more significant than aromatic sulfur. At the same time, only hydroxyl and aromatic ethers in the structure of oxygen-containing functional groups exhibit better thermal stability, even in OSB, at a final temperature of 500 °C. Based on the experimental research, the alicyclic structure was used as a “bridge” and the “archipelago” type molecular structure model of OSB was constructed. After energy optimization, the total energies of DBI and EBI were 6410.08 and 6028.55 kJ mol−1, respectively. The model was compact and stable, showing a more obvious formation of sheet type structure.