Asphaltene aggregation and consequent precipitation have crucial effects on petroleum processing from clogging pipelines in transporting stage to deactivating catalysts in refinery stage. The goal of this work is to probe the effect of mixed organic solvents on asphaltene aggregation, and hence, shed light on asphaltene precipitation from atomic level. A series of molecular dynamics simulations were performed on the aggregation of model asphaltene in heptol (mixture of n-heptane and toluene). The model asphaltene is a mixture of continental-type model compounds with different aromatic/aliphatic ratios. It was found that in pure toluene, the aggregates were small and quite unstable, with the stable average aggregate containing 3 molecules. With increasing n-heptane volume ratio, stability and size of the aggregates were increased, and the stable average aggregate in pure n-heptane contained 8 molecules. In addition, the shape of the aggregates exhibited continuous changes as the n-heptane volume ratio was increase, and transitions from short-cylinder-like aggregates in pure toluene to one-dimensional rod-like aggregates in pure n-heptane was observed. Furthermore, there appear to exist two critical n-heptane volume ratios: one below which the aggregation kinetics was not affected by the small amount of n-heptane present, and one above which the aggregates are dominated by one-dimensional rod-like structures. Correlations were made between simulation results on aggregation and experimental precipitation data.

Aggregation of model asphaltene in heptol investigated by molecular dynamics studies

248th National Meeting (2014)

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