(19c) Measurements of the Association and Stability of Asphaltenes - a Multidiciplinary Approach

The phase separation of asphaltenic constituents of petroleum during production, handling and refinery processing continues to be a challenge. This presentation gives an overview of the application of microcalorimetry, SANS, X-ray diffraction and other techniques combined with the chemical alteration of asphaltenes in order to better understand the stability mechanisms. It is known that association and aggregation are important mechanisms in the formation of asphaltenic sludges. Two types of overall mechanisms, the pi-pi aromatic stacking and the hydrogen bonding, are possible association steps. However, the application of methylation and silylation to asphaltenes, which removes the hydrogen binding sites, clearly indicates that these specific interaction sites may indeed participate in a positive way to prevent sludge formation. For native asphaltenes we have demonstrated that especially SH and NH are important interactions. Hence, during HDS and HDN processes, these stabilizing bonding sites are removed, which may lead to additional instability. The mechanism is currently interpreted as smaller asphaltenes (higher polarity, low MW) interacting with large asphaltenes (lower polarity, high MW) preventing these from associating with large molecules. The presentation discusses the pi-pi stacking and the type of possible ordering of such stacks by comparison with crystal formation in pure polyaromatic components. The presentation also gives an overview of the balance between the various forces involved.