Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 9, pp. 1370−1375.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © E.V. Mal’tseva, A.M. Gorshkov, L.V. Chekantseva, L.V. Shishmina, N.V. Yudina, 2013, published in Zhurnal Prikladnoi Khimii,
2013, Vol. 86, No. 9, pp. 1401−1406.
AND INDUSTRIAL ORGANIC CHEMISTRY
Inﬂ uence of Aggregation of Asphaltenes
on the Rheological Properties of Oil
E. V. Mal’tseva
, A. M. Gorshkov
, L. V. Chekantseva
, L. V. Shishmina
, and N. V. Yudina
Institute of Petroleum Chemistry, Siberian Division, Russian Academy of Sciences, Tomsk, Russia
Institute of Natural Resources, National Research Tomsk Polytechnic University, Tomsk, Russia
Received June 16, 2013
Abstract—Photon correlation spectroscopy was used to determine the threshold concentrations of n-heptane for
phase transitions of asphaltenes in model systems for two types of oil. The rheological properties exhibited by
high-parafﬁ n oil in the asphaltene aggregation process were analyzed. It was shown that the presence of resin
and parafﬁ n fractions in oil prevents phase transition of asphaltenes at the threshold concentration of n-heptane
for the model system, so that a higher precipitant concentrations is required for aggregation of asphaltenes and
formation of oil sludge.
Colloidal properties of oil disperse systems (ODSs)
are determined by the nature, composition, and ratio of
high-molecular-weight components: asphaltenes, resins,
and parafﬁ ns. In hydrocarbon ﬂ uids at fairly high tem-
peratures parafﬁ n waxes occur in molecularly dispersed
state. With cooling and approaching the crystallization
temperature, formation of mobile conglomerates of par-
afﬁ n crystals constituting the spatial framework in oil is
observed [1, 2].
Phase transitions of asphaltenes in ODSs are governed
by their concentration, nature of the medium, temperature,
and pressure. The particle size of asphaltenes exerts a
decisive inﬂ uence on formation of deposits in oil and oil
products. Aggregation in a colloidal system is a nonequi-
librium kinetic process of particle growth [3–5]. Studies
by several researchers showed that the diameter of the
asphaltene particles depends on the initial concentration
and amount of precipitant in the system. The size and
structure of the resultant aggregates are also associated
with the chemical features of asphaltenes and the ag-
gregation dynamics. Asphaltenes owe their ability for
self-association and formation of molecular aggregates
and nanocolloids to high polarity and aromaticity, as well
as to the presence of heteroelements (N, O, S) and metals
(V, Ni, Fe) [4–6].
Previously , the phase transitions of parafﬁ ns in
oil systems were considered. Here, we examined the
aggregation dynamics of oil asphaltenes in relation to
their structural features and rheological characteristics
using the photon correlation spectroscopy technique and
compared the results with the data on aggregation of the
asphaltene fraction in oil.
The objects of our study were asphaltenes isolated
with n-heptane from high-parafﬁ n (HP) and high-viscos-
ity (HV) oils that differ in the composition and physico-
chemical properties (Table 1).
Asphaltene aggregation was studied by photon cor-
relation spectroscopy (PCS) on an asphaltenes-toluene-
heptane model system.
The PCS technique is based on determining the dif-
fusion coefﬁ cient of the colloidal particles by measuring
the spectral composition (or correlation function) of
scattered light. Assuming a spherical particle shape, the
particle radius can be calculated by the Stokes–Einstein
formula [3, 4, 8].
Toluene was used as solvent. The concentration of
asphaltenes in toluene was 0.1 g L
. Asphaltenes were