A better understanding
of the nature of crude oil compounds that
preferentially interact with certain types of solids is essential
to visualize solutions to challenges in oil fields, such as enhancing
the oil recovery factor, via wettability alteration, and remediating
emulsions stabilized by fines, among others. The simplistic assumption
that the organic matter linked to hydrophilic solids corresponds to
polar fractions (i.e., asphaltenes) needs more compositional detail.
In an attempt to elucidate this important issue, in the present work,
the organic species from an oil adsorbed on silica, alumina (synthetic
solids), bentonite, and kaolinite (clays) were isolated and subsequently
identified by infrared spectroscopy and Fourier transform ion cyclotron
resonance mass spectrometry in atmospheric pressure photoionization
positive mode. The solids were characterized by X-ray powder diffraction
and point of zero charge. Interestingly, the nature of adsorbed compounds
depends upon either the surficial charge of the solids or the acidic
character of the functional groups. Through both infrared spectroscopy
and mass spectrometry, consistent and complementary results were achieved.
The preferential adsorption of nitrogen basic compounds on bentonite
and kaolinite was evidenced, promoted by the presence of metal–OH
groups on the clay surface. Furthermore, that compounds adsorbed on
all of the materials had slightly lower aromaticity than asphaltene-type
compounds but an important contribution of oxygen compounds, which
included sulfone-type compounds not detected in the asphaltene fraction.
Highly conjugated aromatic oxygenated species were identified in the
adsorbed organic matter by alumina, while oxygenated acidic compounds
(carbonyl derivatives) were identified in the extracts recovered from
silica, kaolinite, and bentonite.