Asphaltene aggregation studied by molecular dynamics simulations:role of the molecular architecture and solvents on the supramolecular or colloidal behavior

Asphaltene aggregation is a subject under vivid discussion:There are several parameters one needs to determine before its behavior can be mastered and better target solutions can be tailored.The nature of asphaltene aggregation(colloidal or supramolecular)and the role of solvents and their mixtures are among the least understood parameters in asphaltene science.This paper addresses molecular dynamic simulations to correlate the aggregation properties of asphaltenes,their molecular structure and the concentration of these solvents.We show that the formation of the nanoaggregate depends,primarily,on the size of the conjugated core and on the eventual presence of polar groups capable of forming H-bonds.Heteroatoms on the conjugated core do not change their shape or type of aggregation but may induce stronger π-π interactions.The macroaggregation formation depends upon the length of the lateral chains of asphaltenes and also on the presence of polar groups at its end.Moreover,n-heptane and water may interact selectively with asphaltenes in function of their molecular architecture.Given this fact and the aggregation behavior observed,we advocate toward the assumption that a colloidal behavior of asphaltenes might be a particular case of a more general model,based on a supramolecular description.

Role of the porphyrins and demulsifiers in the aggregation process of asphaltenes at water/oil interfaces under desalting conditions:a molecular dynamics study

Breaking water-in-oil emulsions during the refining of crude oils is an important step before any upgrading process is started.Asphaltene molecules are incriminated as playing an important role in this phenomenon.Unraveling the mechanisms behind the affinity between them and water is a key step to understand how to break these emulsions more easily and require lower amounts of demulsifiers.Choosing which demulsifier molecule(s)to use is also primordial,but to do so rationally,one needs to know which are the molecular interactions in place between asphaltenes,porphyrins and water so that demulsifiers are chosen to destabilize a specific physical–chemical interaction.In this paper,we study the interactions arising between asphaltenes and porphyrins and six different molecules potentially displaying a demulsification action in the presence of water/oil interfaces.We demonstrate that the ionic demulsifier molecules present an interesting potential to either interact strongly with water,replacing asphaltenes in this interaction,or to interact with the active sites of asphaltenes,deactivating them and avoiding any asphaltenic interfacial activity.Finally,we also found that although asphaltenes do not migrate spontaneously toward the water/oil interfaces,porphyrins do so rather easily.This indicates that porphyrins do have an important activity at the water/oil interface.