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Apparent disaggregation of colloids in a magnetically treated crude oil
PREPRINT of the paper published in: Energy & Fuels
, V.23, Iss.8, pp.4016-4020 (2009).
Apparent Disaggregation of Colloids in a Magnetically Treated Crude Oil
Igor N. Evdokimov,* and Konstantin A. Kornishin
Department of Physics, Gubkin Russian State University of Oil and Gas,
Leninsky Prospekt, 65, Moscow B-296, GSP-1, 119991, Russia
“The new physical mechanism” of viscosity reduction of petroleum fluids was suggested
in a series of recent publications. The key idea is that magnetic field treatment aggregates
colloidal particles inside a crude oil into larger ones, thus decreasing viscosity. On the basis of
new experimental data and of the analysis of well-proven theoretical models, we conclude that
this “physical mechanism” in magnetically treated oils appears to be non-existent. In particular,
as revealed by our optical measurements, magnetic treatment results in disaggregation of
* To whom correspondence should be addressed. E-mail: email@example.com
Over the past years it has been repeatedly claimed that magnetic/electric field treatment
may have beneficial effects on the properties of crude oils. The most frequently reported were
cases of significant viscosity improvement. Recently, “the new physical mechanism” of viscosity
reduction was suggested in a series of papers in Energy & Fuels and in other publications.1-7 The
key idea is that magnetic (or electric) field treatment aggregates asphaltene (or paraffin) particles
inside crude oil into larger ones. In turn, particle aggregation is the cause of the observed
viscosity decrease. The authors claim that this basic mechanism of viscosity is universal and
powerful for all liquid suspensions with broad applications, present ones and future ones. They
also claim that laboratory tests confirm their theory.
It appears, however, that some of the above statements and conclusions are not justified
and are at odds with established knowledge. The discussed publications give the impression that
the authors may not be familiar with well-known data on asphaltene aggregation effects on
petroleum rheology. In fact, there is multiple and conclusive evidence that aggregation of
asphaltenes (at constant concentration) increases
the viscosity of petroleum. E. g., it is well-
proven, that when asphaltene particles in the stored (degrading) oil become prone to aggregation,
the viscosity of oil increases.8 Back in 1932, Mack9 measured viscosity of Mexican asphalts and
suggested that the significant viscosity increase is due to strong aggregation of asphaltene
particles. In a number of publications it has been concluded that association of asphaltene
particles in crude oil and in vacuum residue can be distinguished by a corresponding increase of
viscosity.10-13 Storm and Sheu14 applied four viscosity models for a colloidal dispersion to
experimental data on viscosity of a vacuum residue and concluded that high viscosity was due to
increase of volume of asphaltene particles. Fenistein et al.15 have shown that viscosity variations
paralleled those of the volume of asphaltene aggregates as determined from the neutron scattering
data. More recent experimental results of Luo and Gu16 again demonstrated that if the dispersed
asphaltene particles aggregate and become large enough, the heavy oil viscosity increases
significantly. Finally, Johansson et al.17 reported experimental decrease of viscosity in asphaltene
solutions and attributed it to disintegration of oligomeric aggregates into monomers. They also
noted that enhanced asphaltene association increased the viscosity of the solution.
It is true, however, that there are insufficient experimental data on long-term changes in
the state of aggregation after magnetic treatment of crude oils, though viscosity reduction has
been observed by many authors.18-27 Some indirect evidence of post-treatment disaggregation was
obtained by microscopy of deposits19-21 and by measuring the number of inhibition (paramagnetic,
etc.) centres.25,27 The direct detailed experiments have demonstrated only temporary orientation
of some petroleum constituents under the action of an applied magnetic field.28-30 In the present
paper we describe experimental studies of a magnetically treated crude oil by optical methods
which have been shown to be sensitive to the state of asphaltene aggregation.31-33
The studied virgin crude oil was collected directly from an oil-producing well
at Aznakayevsky reservoir in Tatarstan, Russia. After water separation, this oil had a specific
gravity (SG) of 0.8756, contained 3.6 wt. % asphaltenes, 1.8 wt. % sulfur, ~6 wt. %
paraffins/waxes. Previously, it has been repeatedly demonstrated that crude oils from this origin
decrease their viscosity after treatment of flowing oils by constant magnetic fields.34, 35
. The experimental set-up was based on a permanent C-shaped
magnet with a high-homogeneity field in the 12 mm gap between parallel circular poles. The
magnetic field strength was 0.12 T as measured by proton resonance meter. In each of eleven
experiments, we employed four 2 ml oil samples in sealed glass tubes inclined by ca. 20o to the
horizontal plane. After filling the tubes, the samples were allowed to equilibrate for 30 minutes.
One pair of samples was placed into the pole gap of the magnet; another pair remained outside
magnetic field. In each pair, one sample remained stationary; the other was rotated with a
frequency of 55-60 revolutions per minute (cf. the scheme of experimental setup in Figure 1).
This oil treatment procedure continued for 1 hour at 20-23 oC; afterwards optical properties of all
samples were measured within 2-3 minutes.
Experimental setup for magnetic treatment of the crude oil (for details – cf. text).
Measurements of Optical Properties
. The refractive index (RI) measurements were
performed in an Abbe-type refractometer IRF-454-B2M (KOMZ, Kazan, Russia).33 For toluene
at 20 oC the measured RI was 1.4967, close to the value of 1.4969 quoted by the producer. The
UV-visible extinction (UVVE) spectra in the 205-535 nm range have been measured with a
Shimadzu UV-2201 UV/VIS double-beam recording spectrophotometer.32 The UVVE data were
collected with 1 nm wavelength increment and automatically stored. The obtained data sets were
computer-processed according to the below described procedures. Extension of UVVE
measurements to larger wavelengths (310-750 nm range) was obtained by studying toluene
solutions of oils in a spectrometer, equipped with a set of narrow-band light filters (KFK-2
Photocolorimeter).31 All optical measurements were performed at 20 oC and at ambient pressure.
Results and Discussion
Experimental evidence of disaggregation in magnetically treated oil
. Table 1 shows
mean values and standard deviations for RI in four types of oil samples employed in our
experiments. In agreement with previously reported studies,18-27 a statistically significant effect
was achieved only in case of magnetic treatment of a flowing (agitated) crude oil. Namely, a
decrease of RI by ca. 0.2% was registered in samples rotated in a magnetic field.
Results of refractive index measurements in magnetically treated and control samples of
a crude oil. Values of specific gravity and of molecular weight are estimated by empirical
1.5380±0.0006 1.5405±0.0007 1.5404±0.0004 1.5403±0.0007
0.8706±0.0012 0.8759±0.0014 0.8756±0.0008 0.8755±0.0014
Multiple experimental studies have proved a strong correlation of RI with a specific
gravity (density, API gravity) and an average molecular weight (AMW) of native crude oils,36-39
which, in turn, are correlated with oil viscosities.40 Accordingly, two bottom lines of Table 1
show the respective values of specific gravity and AMW estimated from experimental RI data by
using empirical correlations from Refs. 37,38. There is an apparent decrease of both SG and
AMW by ∼0.6% and ∼1% by in samples rotated in a magnetic field.
The theoretical expression of RI-density relationship showing closest agreement with
experiment is the formula of Lorentz and Lorenz:41
is the specific refractivity in terms of the refractive index, n
and the density ρ. The
specific refractivity has been shown to be substantially independent of the state of aggregation
and relatively invariant to change in temperature.
36,41,42 Hence, at a constant temperature, the
observed lower RI values in magnetically treated samples may be reliably attributed to well-
known density (specific gravity) decrease in fluids via bond break-up and deaggregation,43,44
Computer simulations have shown that these processes should be accompanied by a decrease of
fluid’s viscosity.44 An exception is a case where colloidal particles are stabilised by strongly
absorbed solvent molecules. In such system structure-breaking in colloidal aggregates is
counteracted by structure-building at the increased interface area; hence the net effect is an
increase of bulk density.45-47 The data of Table 1 suggest that such stabilization/absorption effects
are negligible in a colloidal system of the studied crude oil.
Additional proof of disaggregation in magnetically treated oil was provided by
measurements of optical extinction. Figure 2 shows Shimadzu UV-2201 extinction spectra of
non-treated oil (1) and of a crude oil sample rotated in a magnetic field (2); note a log scale for
extinction. Clearly seen is a decrease of extinction after magnetic treatment at all wavelengths.
The details of this effect were emphasized by computing the ratio of extinction in a treated
sample to extinction in the original crude oil, as illustrated in Figure 3. Solid line – the data from
Figure 2; open circles connected by dashed line – the data from KFK-2 Photocolorimeter.
Optical extinction spectra of the original (1) and of magnetically treated (2) crude oil.
Optical extinction of crude oils is conventionally discussed48,49 within the Rayleigh limit
when extinction cross-section is considered to be a sum of the absorbance and scattering
contribution, σext = σabs + σscatt. Aggregation effects on absorbance were shown to be negligible at
asphaltene concentrations characteristic to non-diluted crude oils,31,32 while the Rayleigh
scattering cross-section is extremely sensitive to any changes in the radii r
2 π ⎛ n
is the wavelength of the incident light and n
is the ratio of the particle RI to the RI of
continuous phase.49 Accordingly, the overall decrease of extinction may be regarded as a
qualitative proof of magnetic field - induced decrease of the size of suspended colloidal particles.
It should be noted, however, that the relative decrease of Rayleigh scattering is expected
to be independent on the incident wavelength, while Figure 3 shows a step-like change from a
value of ∼0.875 below 300 nm, to another fairly constant level of ∼0.95-0.96 above ca. 370 nm.
A plausible interpretation may be a different degree of magnetic action on smaller and larger
crude oil molecules. The most effective absorbers below 300 nm are known to be low molecular
weight species with 1-2 ring aromatic chromophores, while absorbance in the visible and in the
near-IR ranges is due to the presence of heavier asphaltene molecules with multiple-ring aromatic
Relative decrease of crude oil’s optical extinction after magnetic treatment.
The appearance of two local minima in the longer-wavelengths part of Figure 3 may be
regarded as an additional support of the above interpretation as these are indicative of relatively
stronger magnetic field effects on the specific molecular species. In particular, the position of
these minima coincide with positions of the strong Soret and the weaker Qα and Qβ absorption
bands in vanadyl porphyrins51 (at 410, 553 and 573 nm as indicated by vertical lines in Figure 3).
Furthermore, it has been experimentally demonstrated that vanadyl porphyrins are accumulated
only in asphaltene sub-fractions with the lowest molecular weights.
Theoretical models do not support “the new physical mechanism” of viscosity
reduction via particle aggregation
. As discussed in Introduction, the authors of Refs.1-7 claim
that this “basic mechanism of viscosity” is universal and powerful for all liquid suspensions.
However, their theory of this mechanism obviously is the result of false assumptions and serious
misinterpretations. In particular, consider the following statement from Ref. 2 on relation of
viscosity η to the particle size at constant volume fraction φ:
“While a profound theory for this size effect is still lacking, the following qualitative
explanation helps our understanding. Generally, the effective viscosity depends on how much
freedom the suspended particles have in the suspension. The less freedom for the particles, the
faster the energy dissipates and the higher the effective viscosity. The mean free path of the
spheres inside the suspension is given by l
φ), where a is the particle radius. As a gets bigger,
l becomes longer, indicating that the suspended particles have more freedom to move in the
η goes down
This qualitative conclusion of increasing l
with increasing a
may have followed only from
an over-simplified elementary kinetic theory of ideal gases54 with an additional restricting
assumption that primary suspended particles do not flocculate (retaining their identities) into
irregular-shaped aggregates but coalesce into new spherical species. Under these assumptions,
2 where n
is the number density of particles. At constant φ, n
3; hence it may be
In fact, realistic theories of disordered media, free from simplifying assumptions, show
that the larger are the diffusing particles, the smaller is the mean free path at constant volume
Another argument for the new “basic mechanism of viscosity” concerns the behaviour of
a maximum volume fraction, φm, an important “crowding” parameter in a number of models, e.g.
in the Krieger-Dougherty’s formula for effective viscosity of a liquid suspension:57
where η0 is the viscosity of a base liquid and [η] is a so-called intrinsic viscosity (equal to 2.5 for
In Ref.1 the authors of “the new mechanism of viscosity” insist that magnetic field
“aggregates the small particles into large ones. … While this change in rheology does not alter
φm increased as a result of the increase of … average particle size. Hence, the effective
η is reduced
As above, this conclusion obviously comes from misunderstanding of aggregation
phenomena in solid suspensions. An increase of φm with increasing size is possible only in very
rare cases (e.g. in emulsions) where new compact particles (aggregates) are formed by total
coalescence of smaller ones.58,59 In solid suspensions, however, aggregation always proceeds via
flocculation of smaller particles into non-compact clusters (open structures containing entrapped
Since Mooney,60 φm is interpreted as the volume fraction at which particles (aggregates)
fill the available space and the viscosity increases because of mechanical interlocking. For rigid
individual spheres, independent of size, the maximum φm=0.74 is achieved in hexagonal close
packed arrays. However in suspensions of flocculated open clusters space-filling commences at
much lower concentrations of primary particles, i.e. φm decreases
(and effective viscosity
increases) with increasing size. The magnitude of these effects depends on the volume fraction of
int 0.74, as illustrated in Figure 4. Solid curves are theoretical
evaluations of relative viscosity ηrel=η/η0 which have shown a good agreement with
Increase of relative viscosity as a result of particle aggregation in a suspension. Curve
1: primary particles do not form aggregates; curve 2: φint=0.65 (cubic centered packing of
particles inside aggregates); curve 3: φint=0.56 (simple cubic packing of particles inside
Summarizing, the crucial theoretical arguments in Refs. 1-7 supporting the ”basic
mechanism of viscosity” are not justified and are at odds with well-established knowledge in
rheology of aggregating suspensions. Characteristically, some of these publications recently were
also criticized for claims and conclusions that violate the first law of thermodynamics.62
Possible molecular mechanisms of magnetic treatment
. After this paper was submitted
for publication, one of the reviewers requested more discussion for particular chemical
(molecular) mechanisms of magnetic treatment effects in crude oils. Regretfully, literature
analysis shows that at the moment this subject is still under-investigated, hence any suggested
model would be merely speculative. Various mechanisms of magnetic action have been proposed,
but not proven conclusively. E.g., some groups of scientists ascribe a key role to charged species
in petroleum and to arising Lorentz forces which can destroy molecular aggregates.19 Other
authors discuss the magnetic treatment effects in terms of intrinsic magnetic properties of
asphaltene colloids.18,27 Presumably, asphaltene particles may be either ferromagnetic (due to
ferrous micro-contaminants),63 paramagnetic27,64 or diamagnetic.65 However, the implicit
controversy in models with magnetic asphaltenes is that such particles may be expected not to
disaggregate, but to flocculate under the action of a magnetic field.66 Some other molecular
mechanisms are discussed in publications on specially formulated electrorheological and
magnetorheological fluids,67-69 in particular, external field effects on hydrogen bonding.69 In our
previous publication we have discussed the importance of easily disrupted hydrogen bonds in
asphaltene aggregates.70 Hence, a plausible cause of the above discussed disaggregation of
petroleum colloids may be a transient break-up of hydrogen bonds between asphaltene molecules.
Recent suggestion of “the new physical mechanism” of viscosity reduction via particle
aggregation has added unnecessary confusion to a still controversial topic of magnetic field
effects in crude oils. On the basis of the above experimental and theoretical evidence, we may
conclude that this “physical mechanism” in magnetically treated oils appears to be non-existent.
The widespread circulation of scientifically untenable "explanations" does little to inspire
confidence in any beneficial effects of magnetic treatment of petroleum. However, unbiased
experiments increasingly report evidence that magnetic treatment may significantly alter the
colloidal properties of asphaltenes and paraffins in crude oils. Further research is needed to reveal
the true molecular nature of these effects.
The authors are indebted to Mr. I. V. Kovalenko and Mr. A. P. Losev for their assistance
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Dispersions. Energy Fuels 2006
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