Zn(II) Complex Catalyzed Coupling Aquathermolysis of Water-Heavy Oil-Methanol at Low Temperature

Article abstract of DOI:10.1134/S0965544118030039

A Zn(II) coordination complex was synthesized, characterized, and used for catalytic aquathermolysis of heavy oil at low temperatures for the first time. The effects of water content and catalyst concentration on aquathermolysis were investigated. And then a tri-component coupling aquathermolysis of waterheavy oil-methanol was designed and the reaction conditions were investigated. With the catalyst and methanol, the reaction occurred at temperatures as low as 180°C. The viscosity of the product was also substantially reduced from around 24 400 to 6420 mPa s by the decomposition of the large hydrocarbon molecules.

Full text of DOI:10.1134/S0965544118030039

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 3, pp. 197–202. © Pleiades Publishing, Ltd., 2018.
Zn(II) Complex Catalyzed Coupling Aquathermolysis
of Water-Heavy Oil-Methanol at Low Temperature1
Gang Chena, *, Weihua Yuana, Jiao Yana, Mei Menga, Zheng Guoa, Xuefan Gua, Jie Zhanga,
Chengtun Qua, Hua Songb, and Ayodeji Jejeb, **
aCollege of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, 710065 China
bDepartment of Chemical and Petroleum Engineering, University of Calgary, Calgary, T2N 1N4 Canada
*e-mail: gangchen@xsyu.edu.cn
**e-mail: jeje@ucalgary.ca
Received February 15, 2017
Abstract—A Zn(II) coordination complex was synthesized, characterized, and used for catalytic aquather-
molysis of heavy oil at low temperatures for the first time. The effects of water content and catalyst concen-
tration on aquathermolysis were investigated. And then a tri-component coupling aquathermolysis of water-
heavy oil-methanol was designed and the reaction conditions were investigated. With the catalyst and meth-
anol, the reaction occurred at temperatures as low as 180°C. The viscosity of the product was also substan-
tially reduced from around 24400 to 6420 mPa s by the decomposition of the large hydrocarbon molecules.
Keywords: heavy oil, catalytic aquathermolysis, viscosity reduction, coordination complex, methanol
DOI: 10.1134/S0965544118030039
INTRODUCTION
Catalysts may be classified in terms of the phase
within which they are active. A catalyst may be dis-
solved in the oil, suspended as particles in the oil or
dissolved in the water. The oil soluble and dispersed
catalysts are reported to be slightly more active than
the water-soluble catalyst [6–8], but the costs are sig-
nificantly higher than for water soluble catalysts.
Although cheap, common transition metal salt cata-
lyst (molybdenum and nickel water soluble salts, etc.)
is easy to hydrolysis under the condition of pH > 2.8
and transition metal coordination complexes can keep
stable in the condition of pH is larger (pH 7~8 in this
study). Identifying an effective water-soluble catalyst
and the reaction conditions that promote decomposi-
tion of large hydrocarbon molecules to lower the oil
viscosity is a motivation for this study. The conditions
are different from catalytic cracking processes in refin-
eries at elevated temperatures. Aquathermolysis of
heavy oil, catalyzed by water-soluble catalysts,
occurs at relatively mild conditions (160−280°C;
10−25 MPa) and short durations (24−240 h), but the
viscosity reduction is only about 60% [9, 10] and the
product is still viscous. It has been suggested that a
hydrogen donor additive such as tetralin helps to fur-
ther lower the viscosity [11]. Tetralin is, however,
expensive and toxic. Methanol is being tested as an
alternative in this study.
With prospects of light crude oil supplies running
out in the not too distant future, heavy oil and bitumen
are gaining prominence as reliable sources for satisfy-
ing the increasing global demand for fuels and petro-
chemical feedstock. Heavy oil and bitumen reserves
are estimated to account for 70% of the total recover-
able petroleum in the world. However, the viscosities
are high, between 10 and 107 mPa s, and with densities
between 7 and 26 °API, they present challenges for
production and transportation. Flow through pipe-
lines are currently achieved through the use of dilu-
ents, primarily condensates, which are mixed with the
crude oil produced or extracted or heat tracing of pipes
[1, 2].
Changing the chemical composition and charac-
teristics of heavy oils and bitumen in-situ and before
loading into pipelines is attractive because it helps
improve production and saves the cost of purchasing
and transport of diluents, and the processing opera-
tions for their recovery and reuse. In 1982, Hyne,
Clark and their collaborators demonstrated that metal
complexes can accelerate the thermal degradation of
large organic molecules such as asphaltenes in the
presence of water, a reaction they termed aquather-
molysis [3–5]. There are interests in the reaction
within reservoirs when steam is injected and in the
development of catalysts that promote the reaction.
In a previous study [12], a series of transition metal
coordination complexes were prepared from p-chloro-
phenol Mannich base and transition metal chloride.
1
The article is published in the original.
197

198
GANG CHEN et al.
Table 1. The physical parameters of heavy oil from Yumen oil field
η50, mPa s
ρ20, g cm–3
Pour point, °C
Saturated HC, % Aromatic HC, %
51.83 9.66
Resin, %
23.92
Asphaltene, %
14.59
12 500
41.2
0.901
These were applied as catalyst for aquathermolysis of pellets with a Bruker Tensor 37 spectrometer in the
400–4000 cm–1 region. FTIR spectrometer was cali-
brated by 55 mil thick polystyrene (PIKE Technolo-
gies) as reference standard before the analysis.
heavy oil at relatively low temperature. A Ni(II) com-
plex was most effective and it reduced the viscosity of
the oil by more than 70% with a reaction temperature
of 180°C. Nickel is however associated with FCC cat-
alyst deactivation in the oil processing industry. A zinc
complex is being explored in its place.
Catalyzed aquathermolysis of heavy oil [14–16].
Experiments were carried out by introducing pre-
determined mass ratios of water to heavy oil (0 to 0.6),
with a catalyst to crude oil mass ratio (0 to 0.02), into
the reactor. Each mixture was heated to and main-
tained at 180°C for 24 hours. The reactor and the mix-
ture were cooled to about 50°C in a water bath. The
mixture was then poured into a beaker and the oil
decanted for transport properties and compositional
tests.
Product evaluation. The viscosity of the treated
heavy oil was determined using a BROOKFIELD
DV-II + programmable Viscometer at known tem-
peratures. Viscosity reduction for the oil, Δη%, was
calculated from ((η0 – η)/η0) × 100, where η0 and
η (mPa s) are respectively the viscosities of the oil
before and after the reaction [15]. The sample was cen-
trifuged before testing to remove the water in crude oil.
Before using this viscometer, it was calibrated with
reference fluids purchased form Brookfield. and the
method is as following: Pour the Brookfield Standard
Fluid into the Griffin beaker and put the beaker in the
bath; mount the viscometer on its stand beside the
bath and level it; if it is a digital, turn it on, autozero it
and input the spindle code; attach the spindle;
immerse to the appropriate depth the spindle + guard-
leg into the Brookfield Standard Fluid; re-level the
viscometer; turn the bath on and set it up to 25°C then
wait for at least 30 min (1 h recommended) for the
Brookfield Standard Fluid temperature to stabilize;
before taking a reading, recheck the viscometer level-
ing and adjust if necessary; turn the viscometer on
(dial) or the motor on (digital) and take a high-torque
% reading after at least 4 spindle rotations; log reading
details: speed, spindle, torque and viscosity; shift the
speed down (typically half of the initial speed) and
allow the spindle to rotate for a few minutes; take a
lower-torque % reading and log it; calculate the accu-
racy ranges for both speeds, and determine if the read-
ings are within calculated ranges, 1%. Three readings
were made on each sample to check repeatability and
to obtain an average value and the relative error was
within 2.0%. The sample container and quantity are
approximately the same as for the Calibration Stan-
dard. Equilibrate the temperature of the sample to the
temperature designated in the specification ( 1°C).
EXPERIMENTAL
Materials. Petroleum ether, toluene, ethanol,
formaldehyde, p-methyl phenol, diethanolamine, and
diethanolamine were purchased from Tianjin Kermel
Chemical Reagent Co., Ltd (at AR reagent grade) and
were used without further purification. The heavy oil
used for evaluations was Yumen crude oil with no sus-
pended sand particles. Its properties are shown in
Table 1.
Synthesis of the complexes [12–14]. The pathway
for synthesizing the catalyst complex is shown in
Scheme 1. A mount of p-methyl phenol (1 mmol),
formaldehyde (1.1 mmol) and diethanolamine
(1 mmol) was dissolved in ethanol and refluxed for 4 h
with stirring. A methanol solution of ZnCl2 (1 mmol)
was added dropwise and the mixture stirred for
another 2 h. The mixture was cooled to room tempera-
ture and the precipitate formed filtered and discarded.
It is not water-soluble. The supernatant was kept at
room temperature, for 7 days, open to the ambient in
a fume-hood to allow evaporation and slow reactions
that produce the catalyst as fine particles that are sol-
uble in water.
OH OH
OH
N
OH
H
N
CH2O
+
+
HO
OH
2+
OH
OH
ZnCl2
N
2Cl–
Zn
O
H
Scheme 1. Preparation of Zn(II) coordination complex.
Characterization of the complex. Electronic spectra
were recorded in the range 200–400 nm, with spectral
on as standard, on a UV-2600 spectrophotometer
Furthermore, the heavy oil was further analyzed for
(SHIMADZU). FTIR spectra were recorded in KBr structural changes and group compositions. Four
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Zn(II) COMPLEX CATALYZED COUPLING AQUATHERMOLYSIS
199
A
1
1.0
0.8
0.6
0.4
0.2
0
2
1
2
250
300
350
400
200
Wavelength, nm
2800
2000
cm–1
1200
400
3600
Fig. 1. The electronic spectra of ligand and the complex.
(1) ligand;(2) catalyst.
Fig. 2. The IR spectrum spectra of the ligand and the com-
plex. (1) ligand; (2) complex.
compound groups, namely, saturated hydrocarbons,
aromatic hydrocarbons, resins, and asphaltenes
(SARA), were separated by the column chromatogra-
phy-based method according to industrial standard of
China Petroleum SY/T 5119 [16]. Each test run was
repeated three times to check repeatability and the
maximum errors of the product distribution fell within
2.0 wt %. Only the average data were reported herein-
after.
observed indicating the enolisation of C−O followed
by deprotonation and complexation with metal ions.
The wide band around 3334 cm–1 observed in the
ligand moves to 3260 cm–1 in the complexes, suggest-
ing coordination of –OH of the ligand to the metal. It
is concluded that the ligand acts in a monobasic tetra-
dentate manner in the complex [17]. After the
aquathermolysis and before viscosity measurement,
the upgraded crude oil was centrifuge with a speed of
5000 r/min, to remove the water in oil. In the sepa-
rated water, there is no precipitate. So we speculated
that the complex does not transform to ZnS, maybe
due to the high stability of the complex.
Aquathermolysis with no catalyst or methanol. The
effect of mass ratio of water to oil on the viscosity is
shown in Fig. 3 [18]. The presence of water is demon-
strated to cause the reacted oil to have a lower viscos-
ity, and the more water, the greater the reduction
within the range of investigation. The changes were
not significant once the water to oil ratio reached 0.3.
This will be used as a reference concentration. The
data also showed that as the temperature rose, a more
dramatic lowering of viscosity is observed. The oil vis-
cosity is much more sensitive to temperature changes
than to the amount of water present for the reaction.
Elemental analyses of the heavy oil before and after
reaction were performed on an EL-2 (PerkinElmer)
elemental analyzer. The TGA (Thermogravimetric
Analysis) was carried out using a TGA/SDTA851
(METTLERTOLEDO) instrument over the tempera-
ture range of 35–800°C, at a heating rate of 20°C/min.
The measurements were carried out in N2 atmosphere
(flow rate 16.66 cm3 min–1) by using alumina cruci-
bles. The paraffin crystal in the saturated hydrocar-
bons of the heavy oil before and after aquathermolysis
were examined under a BX41-P OLYMPUS polariz-
ing microscope at temperature of 5°C.
RESULTS AND DISCUSSION
Characterization of the catalyst. Electronic spectra
of the Zn(II) complex and ligand, dissolved in metha-
nol are presented in Fig. 1. In the spectra, the complex
exhibits two intra-ligand charge transfer bands in
235–265 nm (high energy) and a ligand to metal
charge transfer band at 285 nm (low energy) which is
probably due to PhO-Zn(II). In order to study the
binding mode of the Mannich base to the metal ion in
the complexes, the IR spectrum of the free ligand
(Mannich base) was compared with the spectra of the
complexes, as shown in Fig. 2. The IR spectrum of the
ligand shows bands in the regions 3266 and 1500 cm–1,
which are assigned to n(O−H) and n(Ph) of the ligand
respectively. The bands due to n(C–O) is located in
Effect of catalyst concentration. The effect of cata-
lyst loading is presented in Fig. 4. The viscosity of the
oil decreased by about 30% compared with the process
without catalyst as catalyst concentration increased
from 0 to about 0.5% mass ratio of catalyst to oil and
then leveled out. The conditions for these experiments
were the water/oil mass ratio of 0.3, and viscosities
were measured at 45°C.
Effect of adding methanol to reaction mixtures.
Methanol was added to a mixture containing water
and oil with a mass ratio of 0.3. The mass ratio of
the regions 1093 cm–1. In the spectra of Zn(II) com- methanol to oil was 3% by weight of the total mass in
plex, the n(C−O) mode of the free ligand is not the reactor. The results are summarized in Fig. 5. The
PETROLEUM CHEMISTRY Vol. 58 No. 3 2018

200
η, mP s
GANG CHEN et al.
Temperature effects are most important for reduc-
ing the viscosity of heavy crude oil, as the results in the
foregoing section illustrate. Aquathermolysis helps
with viscosity reduction at all temperatures but the
effect at temperatures above 60°C, while important,
are not as dramatic. At 45°C, a drop of a viscosity of
24400 mPa s for unreacted oil to 6420 mPa s for
reacted oil, such as shown in Fig. 6, would be import-
ant for lowering transportation costs. At this tempera-
ture, the addition of catalyst and methanol do not
appear to be effective. At the lower temperatures, as
would more likely prevail for surface transportation,
the effects of the reaction with catalyst and methanol
are obvious. In the following, the activity and charac-
teristics of each of the constituents of the reactor are
discussed, starting with methanol.
Blank
Wter/oil = 0
30000
25000
20000
15000
10000
5000
0
Wter/oil = 0.1
Wter/oil = 0.3
Wter/oil = 0.5
Wter/oil = 0.2
Wter/oil = 0.4
Wter/oil = 0.6
45
50
55
60
65
70
75
40
Temperature, °C
Fig. 3. The influence of water on the viscosity of crude oil
after aquathermolysis reaction.
Activity of methanol. Aquathermolysis is repre-
sented by the following reactions (1)−(3):
η, mP s
heavy oil + water → light hydrocarbons
19000
18000
17000
16000
15000
14000
13000
12000
(1)
•
+ СН4 + СО + Н2 + R ,
CO + H2O → CO2 + H•,
R• + Н• → RH.
(2)
(3)
In aquathermolysis, C−S and C−O bonds in oils
components, particularly resins and asphaltenes, may
be cleaved to form radical chains. Active hydrogen
produced in equation (2) is at low concentrations and
the amount is not sufficient to terminate all of the rad-
ical chains formed from heavy oil components. In the
absence of a hydrogen donor, the active chains can
react with each other and produce higher molecular
weight components. Addition of a hydrogen donor,
such as methanol, leads to the decomposition reaction
(Eq. (4)) and production of free radical hydrogen
in substantial quantities to terminate radical chains
[19, 20].
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass ratio of catalyst to oil %
0
Fig. 4. Effect of catalyst concentration on the viscosity.
30000
Water, catalyst and methanol
25000
Water
Water and catalyst
Blank
20000
CH3OH + H2O → CO2 + CO + H•.
(4)
15000
Group composition and elemental analysis. Changes
in group compositions of heavy oil as a result of reac-
tion are shown in Table 2. The amounts of saturated
and aromatic hydrocarbons increased while resins and
asphaltene decreased in a reaction with water, catalyst
and methanol at optimal levels. The result suggests
that dissociation of resins and asphaltenes is primarily
responsible for the increase in saturated and aromatic
content.
10000
5000
0
45
50
55
60
65
70
40
Temperature, °C
Fig. 5. Effect of methanol on the aquathermolysis with
At the elemental level, the oil seems to have gained
carbon while heteroatoms have decreased from 8.3 to
5.3%, as shown in Table 3. The gain in C can be
attributed to the catalyst and methanol added [21].
The increase of content of C may be attribute to
decrease of N, S, and other compositions. The loss of
heteroatoms from the oil may be due to the production
of water-soluble compounds, such as amines, alcohols
and sulphides [22–24].
0.5 wt % mass ratio of catalyst to oil.
results show that the methanol, as a hydrogen donor,
was effective for reducing the viscosity of heavy oils.
The viscosity was reduced to 6420 mPa s at 45°C.
Compared with the results for unprocessed oil, a vis-
cosity reduction of 73.7% was achieved.
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Zn(II) COMPLEX CATALYZED COUPLING AQUATHERMOLYSIS
(a) (b)
201
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
19.1%
21.6%
44.7%
44.7%
350°C
450°C
12.4%
150°C
150°C
350°C
450°C
11.4%
7.2%
5.9%
16.6%
16.7%
0
200
400
600
800
0
200
400
600
800
Temperature, °C
Temperature, °C
Fig. 6. The TG curves of the crude oil before (a) and after (b) aquathermolysis. 0.5% mass ratio of catalyst to oil, 3% mass ratio
of methanol to oil.
100 μm
100 μm
Fig. 7. Photography of paraffin crystal in saturated HC of the heavy oil before (left) and after (right) aquathermolysis. 0.5% mass
ratio of catalyst to oil, 3% mass ratio of methanol to oil.
Thermogravimetric analysis. Thermogravimetric of the longer paraffinic chains were also decomposed
in the aquathermolysis reaction [25, 26].
analysis reveals some changes in volatility of the com-
ponents as a result of the reaction. Results in Fig. 6
show similar patterns for the oil before and after reac-
tion. There is a slight increase in weight loss in the 33
to 150°C temperature range, consistent with a produc-
tion of small amounts of lighter molecules. And the
CONCLUSIONS
In summary, we have developed a new type of cat-
alyst-Zn(II) coordination complex for aquathermoly-
content of the residue above 750°C also changes cor- sis the heavy oil. Using 0.5% catalyst and 3% metha-
nol at 180°C for 24 h, the experimental results show
that the viscosity of heavy oil was decreased by 73.7%,
with 7.61% in the conversion of heavy content to light
content. Further investigation indicate that, the catal-
ysis aquathermolysis could not only enhance the vis-
breaking of heavy oil, but also improve its pyrolysis
and remove some heteroatoms (S, O, and N), and
finally make the flow properties better and the quality
respondingly, from 7.2% without any treatment to
5.9% after treatment.
Paraffin crystals. Below the pour point of the crude
and processed oils, paraffin crystals will deposit and
tend to plug flow lines and filters. Visual observations
suggest that paraffin crystals are larger size and more
numerous in the crude heavy oil than after being pro-
cessed, as shown in Fig. 7. This may suggest that some upgraded. As a catalyst without any poisonous metal
Table 2. Group compositions of oil sample before and after reaction
Oil sample
Saturated HC, %
Aromatic HC, %
Resins, %
Asphaltene, %
Before reaction
After reaction
51.83
58.22
9.66
10.88
23.92
20.33
14.59
10.57
0.5% mass ratio of catalyst to oil, 3% mass ratio of methanol to oil.
PETROLEUM CHEMISTRY Vol. 58 No. 3 2018

202
GANG CHEN et al.
Table 3. Element content of oil sample before and after
reaction
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Composition, %
Oil sample
C
H
N
S
other*
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84.03 10.67 0.25
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ACKNOWLEDGMENTS
This work was financially supported by the grants
from National Science Foundation of China
(21376189) and Scientific Research Program Funded
by Shaanxi Provincial Education Department
(16JS094).
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