1 research outputs found
Characterization of Acid Species in Asphaltenic Fractions by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Infrared Spectroscopy
Despite
significant advances in the characterization
of asphaltenes,
the study of this fraction of crude oil remains challenging for the
scientific community and oil companies. It is well-known that asphaltenes
are responsible for many of the difficulties found in the extraction,
production, transportation, storage, and refining of petroleum. Although
they are defined as the fraction of crude oil that is insoluble in
paraffinic solvents of low-molecular-weight-type n-heptane (C7) or n-pentane (C5), asphaltenes present a great compositional variety, concentrate
a variety of elements (among which nitrogen, oxygen, sulfur, vanadium,
and nickel stand out), apart from hydrogen and carbon, and are distinguished
by grouping the molecules with greater aromaticity of crude oil. Given
its high compositional and structural complexity, associating operational
problems with specific characteristics of asphaltenes is a task that
is still in force. Asphaltenes, in addition to being distinguished
by their high aromaticity, are also known for their acid–base
properties. The acid character varies according to the origin of the
asphaltenes and is related to the presence of carboxylic acids, phenols,
carbazoles, and indoles. The basic character can be attributed to
the presence of amines, amides, and other nitrogen-containing compounds.
Progressing in the detailed compositional characterization of the
polar compounds comprising the n-heptane-insoluble
fraction (asphaltenes) is still a necessary task toward the understanding
of asphaltene aggregation phenomena and the relationship with crude
oil properties, such as interfacial tension and viscosity. In the
present work, the naphthenic acids of the insoluble fractions of five
Colombian crude oils were characterized. The n-heptane-insoluble
fraction was subjected to a washing process affording four subfractions,
named as extractable 48 h, extractable 72 h, and extractable 96 h,
which correspond to the heptane-soluble fractions that were recovered
after each indicated time, and asphaltene 96 h, which corresponds
to the remaining heptane-insoluble compounds after 96 h of washing.
The samples were chosen so that they had a wide range of asphaltene
content that varied from 3.0 to 19.2%. The acid fraction was obtained
from each sample by solid-phase extraction using aminopropyl silica
as an adsorbent material