Investigating the role of asphaltenes structure on their aggregation and adsorption/deposition behavior

Despite the existing literature, the mechanisms of asphaltenes aggregation, precipitation, and adsorption/ deposition in relation to the structural motifs of asphaltenes remains unclear. In this study, the aggregation and adsorption/deposition of asphaltenes extracted from light, medium, and heavy oils, as well as three distinct subfractions of the medium oil asphaltenes were investigated. The role of asphaltenes structure, concentration, sonication time, and precipitant addition on asphaltenes aggregation was investigated. The adsorption/deposition behavior of asphaltenes on gold surface revealed similar dependency on asphaltenes structure as their aggregation kinetics. The measured adsorption/deposition mass of the studied asphaltenes on a gold surface ranged from 590 to 5600 ng/cm2. Light and medium oil asphaltenes, as well as the least soluble subfraction underwent self-association in toluene, whereas self-association was less evident for heavy oil asphaltenes or the most soluble subfraction. Shorter sonication time, increased concentration and n-heptane addition accelerated asphaltenes aggregation, as expected. Diffusion-limited aggregation followed by reaction-limited aggregation kinetics were identified upon n-heptane addition. The more soluble subfractions were found to assist in stabilizing the parent asphaltenes and the less soluble subfractions.