Vanadium in heavy crude and bitumen causes catalyst fouling in upgrading and refining processes. The current study focuses on evaluating the effect of mild thermal cracking on the nature of the vanadium in the thermally treated products. The vanadium can be present as the paramagnetic oxo-vanadyl ion (VO2+), which may or may not be complexed with porphyrin tetrapyrrole macrocyclic structures, and other vanadium species. It is postulated that vanadium also contributes to viscosity, which is influenced by the polar association between the vanadium through complexes that are formed. Athabasca bitumen was thermally converted at 400 °C for reaction times of up to 24 h. A monotonic decrease in viscosity with increase in reaction time was observed. X-ray fluorescence (XRF) analysis also showed monotonic decrease in vanadium content of the thermally cracked liquid products, which decreased from 155 ppm in the bitumen feed, to 148 ppm after 30 min and 27 ppm after 24 h reaction time. Increased coke formation is a critical factor for decreased vanadium concentrations in the liquid products. A qualitative comparison of electron paramagnetic resonance (EPR) spectra indicated a corresponding decrease in the concentration of the oxo-vanadyl ion. A correlation between the EPR and XRF concentration data was also observed. Similar observations were made for the thermal conversion of Athabasca bitumen at 380°C at reaction times up to 27 h. To investigate the nature of vanadium in a bitumen matrix further, a model compound (vanadium phthalocyanine) was added to three different visbroken samples. The vanadium peaks in the EPR spectra of the modified sample shifted from an isotropic to an anisotropic form, indicating molecular association. The viscosity of the mixture increased by 6 and 3 fold for two different cases of addition of the model compound. These observations emphasize the significance of Vanadyl ion content in bitumen and its behaviour during visbreaking.

Investigating the relationship between vanadium content and viscosity of Athabasca bitumen during low temperature visbreaking: Role of the VO2+ ion

255th National Meeting (2018)

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