Study of Aggregation of Tetrameric Acid and its Interaction with Crude Oil Asphaltenes by Isothermal Titration Calorimetry

Tetrameric acids, also called Arn, are a family of molecules present in crude oils and responsible for formation of deposits by reaction with calcium ions. These deposits are detrimental to oil production and therefore the knowledge of Arn and its properties is of paramount importance. In this report Isothermal Titration Calorimetry was used to better understand interaction of Arn with asphaltenes. The study was held under three main topics: ­ The aggregation of Arn in organic solvents; ­ The interaction of Arn and asphaltenes; ­ The interaction of Arn and asphaltene fractions. Fractionation was carried out using silica particles. Arn molecules interact in organic solvents, and the data obtained were consistent with a dimer model. The heats of interaction, when compared per mol of carboxylic functions, were however lower then what is observed for the interaction between Stearic acid molecules. Arn strongly reacts with asphaltenes. However the interaction is weaker, in a basis of carboxylic functions concentration, when compared to the interaction of Stearic acid and asphaltenes. The interactions between Arn and asphaltene fractions were shown to be weaker than for the case of non-fractionated asphaltenes. It was shown however that possibly the components that are strongly interacting with Arn were lost in the fractionation process.