Montmorillonite-catalyzed thermal conversion of low-asphaltene heavy oil and its main components

Abstract

In-situ combustion (ISC) is an enhanced method to recover heavy oil. As its important part, the thermal conversion of heavy oil is affected by the surrounding clay minerals. Montmorillonite is a major type of clay mineral, and its effect was studied with the low-asphaltene heavy oil as the sample. Temperature-programmed oxidation/pyrolysis experiments were developed to study the catalytic effects of montmorillonite on the thermal conversion characteristics of the sample oil and its main components, namely, saturates (S), aromatics (A), and resins (R). The relations between montmorillonite-catalyzed thermal conversions of the low-asphaltene heavy oil and SAR are analyzed. In the pyrolysis atmosphere, the effect of montmorillonite on the oil and its main components was reflected in the pyrolysis area after 400 °C, where the relative reaction rate decreased and the fuel deposition increased. The catalyzed pyrolysis curve of the low-asphaltene heavy oil could be approximated by the weighted sum of the catalyzed pyrolysis curves of its main components. In the oxidizing atmosphere, montmorillonite showed a different effect on the thermal conversion of saturates compared with that of aromatics, resins and heavy oil due to their different molecular structures. In the presence of montmorillonite, the low-temperature oxidation (LTO) peak lagged behind and the high-temperature oxidation (HTO) region was wider for saturates, while both the LTO and HTO peaks advanced for the aromatics, resins, and heavy oil. The catalyzed oxidation curve of the low-asphaltene heavy oil could be approximated by the weighted sum of the catalyzed oxidation curves of its main components in the LTO region, but not in the HTO region because of the change in fuel properties. The relations between montmorillonite-catalyzed thermal conversions of the low-asphaltene heavy oil and SAR are helpful for predicting fuel deposition during the ISC process.