Methanol enhanced catalytic viscosity-reduction of heavy oil by transition metal-Mannich base complex under low temperature

Article abstract of DOI:10.1134/S1070427216110173

A series of transition metal-Mannich base complex was synthesized and screened for catalytic aquathermolysis of heavy oil and the results showed that the Ni(II)-Mannich base complex is the most effective one. The structure of catalyst was characterized by

Full text of DOI:10.1134/S1070427216110173

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2016, Vol. 89, No. 11, pp. 1853−1860. © Pleiades Publishing, Ltd., 2016.
VARIOUS TECHNOLOGICAL
PROCESSES
Methanol Enhanced Catalytic Viscosity-reduction
of Heavy Oil by Transition Metal-Mannich Base Complex
under Low Temperature1
a
a
a
a
Gang Chen *, Weihua Yuan , Huijun Su , Jie Zhang ,
a
a
b
Xuefan Gu , Yun Bai , and Ayodeji Jeje **
a
b
College of Chemistry and Chemical Engineering, Xi’an Shiyou University,
Xi’an Shaanxi 710065, China
Department of Chemical & Petroleum Engineering, University of Calgary,
Calgary Alberta T2N1N4, Canada
e-mail: *gangchen@xsyu.edu.cn; **jeje@ucalgary.ca
Received April 14, 2016
Abstract—A series of transition metal-Mannich base complex was synthesized and screened for catalytic aqua-
thermolysis of heavy oil and the results showed that the Ni(II)-Mannich base complex is the most effective one.
The structure of catalyst was characterized by Fourier transform infrared (FTIR), ultraviolet and visible spectro-
photometer (UV), and the group compositions C/H/N elemental analysis (EL), and thermogravimetric analysis
(TGA) of the heavy oil were also conducted. The viscosity of the heavy oil can be decreased by 82.6% using
1
.0 wt % catalyst with 15 wt % methanol in a reaction under 180°С for 24 h, and the composition analysis shows
that 9.0% asphaltene is converted to resin and saturated HC. The group composition and the element content of
the heavy oil before and after the aquathermolysis reaction were tested and analyzed.
DOI: 10.1134/S1070427216110173
INTRODUCTION
Hyne and Greidanus’s research [4]. In this technology,
aquathermolysis of heavy oil occurs in the oil layer
With increasing demands for energy resources when superheated steam is injected, which can not only
and a serious shortage of conventional hydrocarbon reduce the viscosity of heavy oil, but also the quality can
resources, heavy oil represents a critically important be upgraded slightly [5–7]. However, further research
hydrocarbon reserve [1]. Nowadays, abundant heavy oil
resources have attracted worldwide attention for solving
the problem [2]. However, high viscosity and density
of heavy oil often cause difficulties in its exploiting.
Thus many methods have been developed and adopted
for enhancing oil recovery (EOR), such as thermal
recovery, chemical recovery, microbial recovery, etc.
Among which, the catalytic aquathermolysis method
is one of the most extensive and effective technology
for heavy oil exploitation with great potential [3].
The chemical interactions between steam, heavy oil,
and minerals were described as “aquathermolysis” by
results show that these positive changes can rapidly
regress since the heteroatoms S, N, and O in the heavy
oil molecule can interact with other groups by hydrogen
bonding or Van der Waals forces, and polymerize to
form larger molecules, thus leading to the rapid viscosity
regression.
Combining steam stimulation with a chemical re-
covery technique, catalytic aquathermolysis has been
developed as a new exploitation technology of heavy
oil with great potential [8]. With the energy and power,
provided by the superheated steam, the catalyst can ac-
celerate the pyrolysis reactions and remove some het-
eroatoms of heavy oil, leading to the further improve-
1
The text was submitted by the authors in English.
1
853

1854
GANG CHEN et al.
Table 1. The physical parameters of heavy oil from Yumen oil field
5
0
Pour point, °С ρ20, cm–3
51.2 0.901
η , mPa s
Saturated HC, % Aromatic HC, %
50.87 5.58
Resin, %
19.95
Asphaltene, %
23.6
3
0510
ment of the aquathermolysis effect [9–13]. Obviously,
In this work, changes in the heavy oil before and after
the catalyst plays an important role in this method. A reaction were analyzed systemically.
way of preparation of a suitable catalyst correponding
to the oil properties and final requirements is the key for
this technique [14].
EXPERIMENTAL
Originally, most researchers used transition metal
salts, transition metal compounds, and organometallic
compounds in this technology [15–17], and later began
to use solid super acids. All this kinds of research
provided a new way to develop the catalyst used in
catalytic aquathermolysis, but the most of them were
far from implementation of this technology. Some
scientists simultaneously studied the mechanism of
catalytic aquathermolysis [18–20]. They pointed out
that the heteroatom (N, O and S)-containing groups in
heavy oil could cause the polymerization, create the
hydrogen bonds and finally lead to high viscosity. So,
breaking the heteroatom-containing groups would be an
efficient way to reduce the viscosity. Nearly all of these
researches supported the mechanism according to which
the catalysts mainly catalyzed the cleavage of the C–S
bonds and that was the main reason why the viscosity of
heavy oil was at last reduced. But in our later research,
it was found that besides the cleavage of C–S bonds, the
catalyst mainly caused changes in oxygen containing
groups, that is, the cleavage of C–O bonds in phenolic,
ethereal molecules, etc. of the heavy oil [21]. To date,
many studies had shown that transition metal ions (serve
as catalytic center) with suitable ligands could promote
the aquathermolysis reaction [16]. With the participation
of transition metal ions (which attack the heteroatoms
of the macromolecules in heavy components of the
heavy oil), the C–R (R = S, N, O, etc.) bonds will be
weakened and the superheated water interaction with
these bonds could be facilitated successfully. Certain
catalytic activity of several transition metals such as
Fe(II, III), Cu(II), Ni(II), Cr(III), Mo(VI), Co(II) has
been confirmed [17]. The ligands are also crucial to the
catalytic performance and serve as the carrier of metal
ions to reduce the viscosity of heavy oil. In our research,
we synthesized a series of efficient catalysts and
conducted the corresponding catalytic aquathermolysis
experiments on heavy oil under relative low temperature.
Materials. Petroleum ether, toluene, ethanol, form-
aldehyde, p-chlorophenol, morpholine were purchased
from Tianjin Kermel Chemical Reagent Co., Ltd (AR
grade) and were used without further purification. The
heavy oil used for evaluations was Yumen crude oil,
properties of which are shown in Table 1.
Synthesis and characterization of the catalyst.
p-Chlorophenol, morpholine and formaldehyde were
dissolved in ethanol in a 1 : 1 : 1 mol ratio and refluxed for
4
h. Then the transition metal chloride ethanol solution
was added dropwise and the mixture was refluxed for
another 4 h, filtered and concentrated in the filtration
under vacuum pressure. The products were obtained
after recrystallization in ethanol. The preparations of
the transition metal-Mannich base complexes and their
names are shown in Scheme 1. The selected catalyst
was characterized by Fourier transform infrared
spectroscopy (FTIR, Nicolet 5700) and Ultraviolet and
Visible Spectrophotometer (UV, Shimadzu UV-2600).
Aquathermolysis reaction. All the experiments
were carried out by adding successively of 30 g oil,
certain amount of water in a designed mass ratio, and
catalyst into the reactor (150 mL). Then the reaction
mixture was heated to the 180°С for aquathermolysis
reaction. After 24 h performing experiments, the heating
was stopped, and then, the reaction mixture was cooled
to about 50°С, dumped in a beaker and water was de-
canted. Thereby the oil sample was obtained to be tested
and analyzed.
Evaluation and analysis of the heavy oil. The
viscosity of the treated heavy oil was recorded by a
BROOKFIELD DV-II + programmable Viscometer at
different temperature. The ratio of viscosity reduction
Δη (%) was calculated as follows: Δη = [(η – η)/η ] ×
0
0
100, where Δη is the rate of viscosity reduction, η is the
0
viscosity of the oil before the reaction (mPa s), and η is
the viscosity of the oil after the reaction (mPa s) [15].
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METHANOL ENHANCED CATALYTIC VISCOSITY-REDUCTION
1855
Scheme 1. Synthesis of transition metal-Mannich base complexes.
H
N
N
OH
O
Cl
OH +
+ HCHO
Cl
O
N
O
O
MClx
M
Cl
(H O)
2
xx
M , M = Fe(III); M , M = Ni(II); M , M= Cu(II);
1
2
3
M , M = Zn(II); M , M = Co(II).
4
5
Three readings were made on each sample to check
repeatability and to obtain an average value and the
relative error was within 2.0%. Furthermore, the heavy
oil was further analyzed for structural changes and group
compositions. Four group compositions, including
saturated hydrocarbon (saturated HC), aromatic
hydrocarbon (aromatic HC), resin, and asphaltene, were
separated from the sample by a chromatography column
according to the industrial standard of China Petroleum
SY/T 5119. The elemental analyses for oil samples
before and after reaction were determined by elemental
analyzer (ESI 1800, Vario MICRO CUBE). The Ni(II)
was extracted from heavy oil according to the method
reported in [22]. Then it was quantitively analysized
using ion chromatography method [23]. The difference
of the saturated HC before and after aquathermolysis
was described by gas chromatography (GC, Shimadzu
GC-2014C). The change of the oil sample quality before
and after reaction, in the process of heating up, was
evaluated by thermogravimetric analysis (TGA, Mettler
e
TGA / DSC1 STAR System).
RESULTS AND DISCUSSION
Characterization of the Catalyst
FTIR characterization. The FTIR spectrum of the
ligand and Ni(II)-Mannich base complex is shown in
Fig. 1. The bands at 3350, 3120, and 1650 cm–1 were
assigned to the stretching and bending vibrations of the
O–Hofphenylgroupandtheassociatedwatermolecules.
–
1
The bands at 1480, 1610, and 2850 cm , moved to
–
1
1
490, 1650, and 2930 cm , respectively, exhibit a red-
shift compared with the absorption wavelength of the
ligand. That could be attributed to the complexation
between ligand and nickel metal ions [15]. As a result,
the prepared catalyst agrees well with what we have
designed.
UVcharacterization. The UVspectrum of the ligand
and Ni(II)-Mannich base complex is shown in Fig. 2.
According to the Fig. 2, because of the n-p* electron
transition, the complex shows an absorption wavelength
at 289 nm, and exhibits a red-shift of 4 nm compared
with the absorption wavelength of the ligand, and the
absorption intensities increases evidently. It indicates
that a stable Ni(II)-Mannich base complex has formed
[24].
Fig. 1. Infrared spectra of the catalyst and its ligand.
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1856
GANG CHEN et al.
this figure, it is found that the viscosity decreased most
effectively with 30% of the water. So in the following
work the dosage of water was fixed at 30% [21].
1
2
Catalyst
Ligand
Catalyzed aquathermolysis. Using the synthesized
complexes as catalysts (in 1.0% of the crude oil quality)
with water (in 30% of crude oil quality), catalytic
aquathermolysis of the crude oil was conducted, and the
results were shown in Fig. 4. As can be seen from Fig. 4,
not all the five complexes were active in this process: M1,
M2, and M4 were effective, among which M2 [Ni(II)-
Mannich base complex] was the most effective with the
viscosity reduction from 182000 to 60000 mPa s, while
M3 and M5 can lead to viscosity rising. So M2 was used
in the following work.
Fig. 2. Ultraviolet spectra of the catalyst and its ligand.
Catalytic Aquathermolysis
Figure 5 shows the effect of the dosage of the catalyst
(M2) on the viscosity of catalytic aquathermolysis heavy
Mass ratio of water to oil. First of all, the reaction
oil. With the increase in the dosage of the catalyst, the
viscosity reduction efficiency increased rapidly. The
rate of viscosity reduction reaches 67.2% (45°С), while
the concentration of the catalyst is 1.0%.
condition should be concerned. So in the first step, the
mass ratio of water to oil was investigated without any
catalyst, and the results were summarized in Fig. 3. From
Fig. 3. Influence of water dosage on the viscosity thermal degradation crude oil.
4
6
1
2
5
3
Fig. 4. Influence of complexes on the viscosity of catalytic aquathermolysis heavy oil.
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METHANOL ENHANCED CATALYTIC VISCOSITY-REDUCTION
1857
Fig. 5. Effect of catalyst on the viscosity of catalytic aquathermolysis heavy oil.
Fig. 6. Influence of different dosage of methanol with the change of temperature on the viscosity of catalytic aquathermolysis heavy oil.
Additives for catalyzed aquathermolysis. It has
been reported that added hydrogen donor additive is
an effective way to enhance the viscosity reduction.
When there is hydrogen donor additive (such as tetralin)
in the reaction system, the tetralin can release free
radical hydrogen, which can react with the active chains
formed in the processes of aquathermolysis and restrain
the polymerization [25]. But the product of tetralin,
naphthalene, is expensive and poisonous to human
beings, so it is important to find some alternates. The
research has revealed that methanol steam reforming
7 show the impact of the methanol-catalyst on the
viscosity of the catalytic aquathermolysis heavy oil. It
was found that the viscosity was reduced further, with
the increase in dosage of methanol. As the dosage of
methanol reaches 15.0% (weight percent of the heavy
oil) the viscosity reduction ratio may reach as high as
82.6% (45°С). With increasing the amount of methanol,
no obvious changes happened.
Change of the Group Compositions
before and after Reaction
(
CH OH + H O) can produce H under high temperature
3 2 2
[
26]. So we employed methanol as a hydrogen donor
The group compositions of heavy oil before and
after reaction were listed in Table 2. It can be seen that
additive in this reaction system, and Figures 6 and
Table 2. Group compositions of oil sample before and after reaction
Oil sample
Before reaction
After reaction
Saturated HC, %
50.87
Aromatic HC, %
Resin, %
19.95
Asphaltene, %
23.6
5.58
9.66
51.83
23.92
14.59
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1858
GANG CHEN et al.
the amount of asphaltene decreased by 9.01%, while
the amount of saturated HC, aromatic HC, and resin
increased by 0.96, 4.08, and 3.97%, respectively, after
reaction. It reveals that the reduced part of asphaltene
was depolymerized to the other tree compositions.
But apparently, the content of light saturated HC and
aromatic HC is not abundant enough for keeping oil
fluidity, and the oil is a solid gel at ambient temperature
[27].
Fig. 7. Effect of methanol dosage on the viscosity of catalytic
aquathermolysis heavy oil (45°С).
Element Content of Oil before and after Aquathermolysis
Elemental analysis results of oil samples before and
after aquathermolysis were listed in Table 3. We can find
that the content of heteroatoms in oil samples is about
1
0.80 and 6.46%, respectively. This reveals that many
free radicals will be generated during aquathermolysis
by cleavage of C–R (R = S, N, O) bonds, which can react
with water and/or methanol molecular resulting in the
decrease in asphaltene and increase in H/C ratio, thereby
improving the quality of the heavy oil [28]. Besides,
the contents of Ni(II) in heavy oil before and after
aquathermolysis in the present of catalyst and methanol
were also determined by using ion chromatography
method. The results showed that the contents of
Ni(II) in heavy oil before and after aquathermolysis
in the presence of catalyst and methanol was 36.4 and
–1
3
0.1 μg g , respectively. The decline can be due to
the higher solvability of the Ni(II) species in hot water
especially combined with an amount of methanol.
Gas Chromatography (GC) of the Saturated HC of Oil
Samples before and after Reaction
ThegaschromatographyresultsofthesaturatedHCof
oil samples before and after reaction are shown in Fig. 8.
It can be seen that the types of the saturated HC have no
obvious changes before and after aquathermolysis. This
factisconsistentwiththeresultofthecompositiongroups
analysis. It is clear that many reactions happen during the
aquathermolysis that is pyrolysis, hydrogenation, ring
opening, ring closing, and desulfuration. Asphaltene
is further aggregation of resins. A fused aromatic ring
system as the core structure is the basic structural unit
of resin and asphaltene molecules. Therefore, hydrogen
bonding or Van der Waals forces between molecules may
be broken, which happened during the depolymerzing
of asphaltene, and led to the viscosity reduction, as
shown in Fig. 9 [29]. Also, one end of the molecular
chain of asphaltene may be broken and generate some
Fig. 8. Gas chromatograph of saturated HC of the crude oil
before and after reaction.
Table 3. Element content of oil sample before and after
reaction
Composition, %
Oil
sample
Ni(II)
μg g
n /n
H
C
–1
C
H
N
S
others
Before
77.31 11.89 0.45 0.42 9.93 1.85 36.4
reaction
After
80.34 13.20 0.32 0.36 5.78 1.97 30.1
reaction
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METHANOL ENHANCED CATALYTIC VISCOSITY-REDUCTION
1859
S
S
Catalyst
C H
n 2n
+
O
O
N
N
S
S
Catalyst
*
*
*
*
O
O
5
~7
2~
3
N
N
Fig. 9. The reactions may happened in the asphaltene during the aquathermolysis.
low molecular hydrocarbon. Because of the low boiling
point, the products may be lost by vaporization when the
oil samples were treated. So no significant changes are
reflected in the gas chromatogram.
donor [31], their synergistic effects would improve the
dispersion and thereby enhance the catalyst, such as
hydrogenation and hydrodesulfurization, etc. Because
even a small fraction of bond breakage can lead to huge
improvement of the flow properties, the total actions
of the catalyst will enhance the cleavage of some C–X
bonds in the oil molecules [28].
Thermogravimetric Analysis (TGA) of Oil Samples
before and after Reaction
TGA was used to analyze the change of the composi-
tions before and after reaction (Fig. 10). There is obvi-
ous difference between the two curves. Before 200°С,
the weight loss of the oil after reaction is much more
than that of the oil before reaction. When the tempera-
ture reached 600°С the residual substance content of oil
sample was 16.1% and 9.9%, respectively. It illustrates
that the heavy composition has decomposed and depo-
lymerized to lighter ones, and the light compositions in-
creased correspondingly, the performance of the macro
is viscosity reduction. This result is consistent with the
composition groups analysis and elemental analysis.
CONCLUSIONS
Insummary,wehavedevelopedanewtypeofcatalyst,
and used it for catalytic aquathermolysis of heavy oil
in the laboratory under relatively low temperature. For
its excellent catalytic activity, the results show that the
viscosity of the heavy oil could be decreased by 82.6%
using 1.0 wt % catalyst and 3.0 wt % methanol under
1
80°С for 24 h, with 9.01% conversion of asphaltene to
other composition. Further analysis of the structure and
group compositions indicates that the reaction could not
only reduce the viscosity of heavy oil, but also remove
some heteroatoms from its molecules, finally making
the flow properties better and upgrading the quality.
Mechanism
Asitisknownthatnickel(II), atransitionmetalcation,
can arouse the dynamic inductive effect in some polar
bondsofasphaltenebytheelectrostaticeffect[30], which
will reduce the active energy of adjacent C–X bonds
(X = N, O, S, etc.), thereby leading to the breakdown
of some C–X bonds. And following the principle of soft
and hard Lewis acids and bases (HSAB), nickel(II) is
also a borderline acid, which is likely to interact with
the soft, borderline, and hard bases (such as N, O, and
S-containing groups), leading to the pyrolysis of some
C–X bonds. Furthermore, as the benzene ring on one
side of the compound could increase the oil solubility of
the catalyst, and the methanol could act as a hydrogen
Fig. 10. TGA of oil samples before and after reaction.
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1860
GANG CHEN et al.
15. Cordova, J., Pereira, P., Guition, J., Andriollo, A.,
ACKNOWLEDGMENTS
Cirilo, A., and Granadillo, F., US Patent 6043182, 2000.
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