Oil sand pyrolysis: Evolution of volatiles and contributions from mineral, bitumen, maltene, and SARA fractions

Abstract

In order to investigate the pyrolysis behavior through the volatile evolution, pyrolyzer-evolved gas analysis-mass spectrometry and thermogravimetric analysis-mass spectrometry were adopted for in situ analysis and comparison the pyrolytic volatiles derived from two different oil sands as well as their mineral, bitumen, maltene and SARA fractions. For both oil sands, the weight loss and volatile release during the oil-producing process exhibited two stages: a devolatilization stage (<350 °C) and a thermal-cracking stage (350–600 °C). These two stages afforded different volatile yields and displayed distinct activation energy distributions. Additionally, heart-cut analysis indicated that the volatiles were in disparate compositions at each stage. The volatile evolution of the oil sand bitumen, maltene, and SARA fractions revealed individual contributions on volatile release with increasing pyrolysis temperature. Specifically, volatiles in the devolatilization stage predominantly originated from the saturates in maltene. These resulted in a significant amount of polycyclic biomarkers and contributed toward the release of higher-molecular-weight substances over a temperature range of 200–350 °C. The thermal-cracking stage was the main stage in which most of the gaseous and light pyrolytic products, including amounts of alkanes and olefins, were generated. These compounds mostly originated from cracking of resin and asphaltenes. The aromatic fraction was observed that released volatiles in both stages. Thus, due to the disparity in temperature region for volatile release, the volatile yields during the different stages of the process were mainly determined from the organic constituents of the oil sand. Notably, the volatile compositions predominantly correlated to the original organic structures. Moreover, the minerals exhibited little influence during the oil-producing stage of the two oil sand samples under the tested heating conditions. However, the presence of interactions between these organic sub-fractions during oil sand pyrolysis is suggested.