Asphaltene and Maltene Adsorption into Graphene

摘要

In this work, the mechanism by which insoluble asphaltenes represented by small graphene fragments interact with different components of crude oils is explored. Adsorption isotherms of maltenes and asphaltenes into graphene from toluene were determined by the depletion method. The results indicate that the adsorption of these heavy fractions occurs in two steps: after the initial adsorption, a plateau is reached that seems to follow a Langmuir type adsorption isotherm. In the second step, at higher concentrations, the adsorbed amount starts to increase sharply after an inflection point indicating strong interactions between the adsorbates. A multilayer adsorption model was successful in describing this adsorption behavior. Dispersion of graphene in the solution was observed for some of the samples in the concentration range studied. It was found that asphaltenes can disperse graphene at lower concentrations than maltenes. From the same crude oil, it was observed that heptane-extracted asphaltenes disperse graphene at lower concentrations than the pentane-extracted ones. Mass spectrometry analysis of the species of molecules left in the solution after adsorption shows the preferential adsorption of highly aromatic molecules, high molecular weight molecules, and molecules containing several heterbatoms. A reduction of 92% on the relative abundance of porphyrins points to a great affinity of these species to graphene. These results indicate that graphene-like molecules in hydrocarbons cannot remain in solution unless they are dispersed by other components. Therefore, the existence of a critical nanoaggregate concentration for these crude oil components is unlikely.