Irreversible Adsorption of Asphaltenes on Kaolinite: Influence of Dehydroxylation

The adsorption of asphaltenes on dehydroxylated mineral surfaces is an important occurrence during thermal processing of unconventional oil resources such as oil sands bitumen. We investigated the irreversible adsorption of Athabasca asphaltenes from toluene solutions onto untreated and dehydroxylated kaolinite. The adsorption density, percent surface coverage, and mean domain thickness were evaluated using X-ray photoelectron spectroscopy (XPS) and elemental analysis. The dehydroxylated kaolinite gave higher adsorption density and percent surface coverage than the untreated kaolinite, as particularly revealed in multiple contacts of kaolinite with the asphaltene-in-toluene solutions (2 g/L), indicating that dehydroxylation of kaolinite enhanced its adsorption capacity for asphaltenes. The XPS-determined percent surface coverage was 18% and 41% on the untreated and dehydroxylated kaolinite, respectively, corresponding to the maximum adsorption density of 3 and 7 mg/m 2 . The incomplete coverage even at the highest adsorption density proved that the asphaltene adsorption layer was discontinuous on both materials. After saturation of kaolinite binding sites with the first asphaltene layer, at most two additional layers were adsorbed due to asphaltene-on-asphaltene deposition, forming 15 nm thick domains.