st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Hydrogen Production from Waste Oil by In-liquid Plasma Method
S. Nomura1, S.Mukasa1, and H.Toyota1
1
Department of Mechanical Engineering, Ehime University, Ehime, Matsuyama, Japan
Abstract: This research creates hydrogen by using in-liquid decomposing waste oils such as
n-dodecane, engine oil and oils used for cooking. There is approximately 65% to 89% hydrogen in the gas generated by plasma decomposition. The hydrogen created from oils uses
ap-proximately 10% of the theoretical amount needed to create it from water, but only 6.8 –
66.3% of the making power is used for the chemical reaction. The hydrogen that was separated and collected from the gas generated was used in an experiment with an internal hydrogen
combustion engine vehicle and successful operation was achieved.
Keywords: in-liquid plasma, hydrogen production, hydrogen vehicle, plasma in liquid
1. Introduction
Hydrogen exists in various raw materials and in some
waste materials. Its biggest appeal is that if hydrogen can
be used for fuel, water could become a source for it.
While there are fundamental technical issues that have to
be addressed, such as how to store and transport the hydrogen, it is an energy source that could solve environmental and resource problems in a world with low carbon
fuel resources. Hydrogen is not a primary energy source
like coal, oil and natural gas, which exist in nature. Rather,
it is a secondary energy source that is obtained by processing a primary energy source. Accordingly, energy is
required to extract and capture hydrogen.
In this research a microwave in-liquid plasma device
with the ability to circulate the liquid was developed and a
method for continuously producing hydrogen by the decomposition of waste oil is proposed. Next, the pressure
inside the device and the shape of the antenna were
changed and tests were conducted. A comparison was
made the hydrogen production ratio of this method with
that of the electrolysis of water. At the end of this research
the gas generated by this device was collected, separated
and tests were conducted on using it to operate a hydrogen powered car.
gas-liquid separator and collected by the downward displacement of water method. At this time, the rate of gas
formation v [mL/s] and an analysis of the properties of
the generated gas were evaluated. Two valves connected
to the input hose for the glass vessel and the bypass hose
were used to adjust the flow volume of the liquid. The
liquid passes from the gas-liquid separator through an
activated carbon filter and into the reservoir tank. The
pressure inside the liquid reservoir tank is reduced by the
air separator. The solidified carbon generated at the time
of decomposition is circulated with the liquid, but nearly
all of it becomes trapped in the activated carbon filter.
In order to be able to change the electrical output of the
microwave oven, the power supply voltage was controlled
by a transformer and the amount of electrical input into
the microwave oven was measured by a watt meter. The
input power for the microwave oven and the power consumed by the aspirator (173 W) and the input power for
operating the pump for circulating the water (100 W)
were recorded as input power Pall . In addition, 500 ml of
water was put in the reactor vessel and the rise in tempergas collection
substitution gas
2. Plasma decomposition Experiment using a liquid
circulation device
Fig. 1 shows a schematic diagram of the experimental apparatus. With the exception of the piping used
for extracting exhaust gases mounted on the top of the
device, this reactor has nearly the same design as a conventional microwave oven. An approximately 550 ml
heat-resistant glass vessel was placed in the microwave
oven and used as a glass vessel [1]. Seven antennas with 2
mm copper rods, were placed on a copper plate [Fig. 3(a)].
The ends of the antenna concentrate the electrical field for
generating the plasma. A pump was used to circulate the
liquid from the reservoir tank inside the device. The gas
that was expelled by the plasma was separated by a
gas-liquid
separator
Activated
charcoal filter
aspirator
bypass
transformer
reservoir
tank
pump
microwave oven
glass vessel
electrode
Fig. 1 Plasma decomposition device with recirculating
device for waste oil
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Table I Comparison of the analysis results of the gas generated and the hydrogen manufacturing performance
Pressure
Pnet
Liquid
(kPa)
n-dodecane
H
η net
ｔ
101
(mL/s)
H2
CH4
C2H2
C2H4
492
15
84.8
2.6
9.6
3
369
14.4
84.6
2
10.5
2.9
118
8.4
88.6
2.8
6.6
2
101
CO
10.9
83.1
1.4
13.1
1.4
0.4
65 - 75
-
-
-
76.1
1.2
12.2
CO2
(kJ/mol)
(%)
(%)
49.9
6.8
41
52.4
9.1
53
42.2
14
101
0
N/A
N/A
29
-
-
-
-
-
1.8
7.8
0.3
N/A
N/A
27
-
-
-
N/A
492
Waste
-
Fresh
cooking oil
Contents of produced gas (%)
(W)
Fresh
engine oil
εｎｅ
v
101
10.9
492
Waste
-
65 - 75
ature after 60 s of operating the microwave oven was
measured. This was then used to find the net power Pnet
being supplied to the inside of the reactor vessel.
Table 1 shows the relative volume of each of the component gases included in the generated gas. With
n-dodecane there is approximately 85% to 89% hydrogen
in the gas generated by plasma decomposition. Low-grade
flammable hydrocarbon gases, such as methane, ethylene
and acetylene were also generated. The ratio of acetylene
was higher in experiments using engine oil or cooking oil,
but nearly all of the gas generated was hydrogen. Because
cooking oil includes oxygen, carbon monoxide and carbon dioxide were also detected. Experiments were also
conducted using waste cooking oil and waste engine oil.
The purity of the hydrogen included in the generated
gases was measured and found to be 65 to 75% pure hydrogen. While the purity of the hydrogen was somewhat
lower, the liquid could be broken down by plasma without
problem.
With n-dodecane, when only four types of gasses (H2,
CH4, C2H2, C2H4) shown in Table I are generated, the
ratio of carbon atoms and hydrogen atoms found in the
gas is 1:0.462. There are carbon atoms that have not been
included in the generated gas. The following shows the
chemical reaction formula when all the carbon atoms
changed into graphite.
aC12H26→ nH2H2+ nCH4CH4 + nC2H4C2H4 + nC2H2C2H2 +
bC(s)
(1)
However,
a = (2nH2 + 4nCH4 + 4nC2H4 + 2nC2H2) / 26
(2)
b = 12a - (nCH4 + 2nC2H4 + 2nC2H2)
(3)
Where, the molecular ratio nH2 :nCH4 : nC2H4 : nC2H2 are as
shown in Table I. The enthalpy of formation per 1 mole of
gas in the chemical reaction in Eq. (1) , ΔH, is shown in
-
-
-
-
-
Table I. The following formula shows the energy efficiency ε, which is the ratio of the energy consumed in the
chemical reaction per unit of time in relation to the power
Pnet input.
v H
VP
100(%)
(4)
Where, V is the standard mole volume (22.4 L/mole), v is
the gas generation speed generated by plasma decomposition. ε will be between 6.8 and 14%. The amount of gas
generated at 118 W with n-dodecane has the highest efficiency with 0.23m3 of hydrogen gas being generated.
The efficiency of hydrogen gas generation was compared with alkaline water electrolysis, which has already
been commercialized. The amount of hydrogen gas per
unit of input energy is a multiple of the hydrogen ratio for
gas generated by v/P. In contrast, based on Table 1, since
the required enthalpy for creating 1 mole of hydrogen
from water is 286kJ/mole and the energy efficiency of
alkaline water electrolysis is approximately 80%, this
would be 6.27×10-2 mL/J. Hence, the efficiency for electrolysis, η is
v n H2
6.27P
100 (%)
(5).
When the output is low, the in-liquid plasma method is
approximately the same as that of alkaline water electrolysis. However, when the output is increased, the majority
of the input energy is used for raising the temperature of
the liquid and η becomes smaller.
Here, when Pall is used Eqs. (4) and (5), which takes
into consideration the pressure reduction equipment and
the operating power of the circulating pump into consideration, η stops at 30% of electrolysis.
3. Plasma decomposition experiments under reduced
pressure
As it has been confirmed that the generation of the
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Table II Comparison of the analysis results of the gas generated under reduce pressure
Pressure
P all
P net
v
(kPa)
[W]
[W]
[mL/s]
1173
488.1
31.3
64.2
5.4
17.5
12.8
773
335.4
19.2
57.3
6.4
16.2
220.1
25.6
61.2
6.0
328
115.0
13.5
59.6
1173
488.1
33.3
743
335.4
515
399
Vertical
Type
80
Fig3(a)
ΔH
ε all
η all
ε net
η net
(kJ/mol)
(%)
(%)
(%)
(%)
74.2
8.8
27.3
21.2
65.7
19.9
76.4
8.5
22.7
19.5
52.3
17.0
15.8
75.2
17.4
50.8
39.0
113.5
6.0
16.1
18.2
75.1
13.8
39.2
39.4
111.6
64.8
4.9
27.8
10.9
98.6
12.5
29.4
30.0
70.5
20.8
75.4
3.2
16.9
7.6
70.7
10.6
40.4
19.6
74.6
220.1
18.5
67.4
4.4
30.5
9.8
105.0
16.5
37.9
39.4
90.4
115.0
16.7
65.8
4.7
29.1
10.9
102.2
22.4
51.6
66.3
152.4
Contents of produced gas (%)
H2
CH4
C2H2
C2H4
4934
93
Curvature
type
80
Fig.3(b)
breakdown gases has a tendency to increase when the
pressure inside the vessel drops, experiments in plasma
decomposition under reduced pressure were conducted.
Fig. 2 shows the experiment equipment. The same microwave generator, glass vessel, antenna and other components were the same as before, but the liquid was not
circulated so that effects of only the reduced pressure
could be examined. An aspirator was used to reduce the
pressure inside the glass vessel. The gases that have been
produced by the plasma are sent together with the flowing
water of the aspirator to the tank where they are collected.
The pressure inside the glass vessel is reduced to approximately the vapor pressure of water prior to the generation of plasma. However, due to the relationship between the amount of gas formed and the amount of gas
expelled from the separator once the plasma has been
generated, the pressure is measured once it has stabilized.
The results of the experiment are shown in Table II. The
generation speed of the gas is approximately up to two
times greater under reduced pressure. When the pressure
is lower, the temperature of the electrons increases. The
ratio of electrons that have enough kinetic energy for
chemical reaction increases.
The results of the analysis of the formed gas show that
there were almost no differences between due to the output in the experiments that used the circulating device
shown in Fig. 2. However, when these results are compared with the experiments in the previous section, the
percentage of hydrogen decreased to 57 - 64% and the
percentage of hydrocarbons increased. C2H4 increases
dramatically. A large amount of "char" remained in the
oven because the liquid inside the glass vessel and was
not circulated. This is because the carbon component inside he reactor oven reacts with the hydrogen generated by
the decomposition, increasing the amount of the hydro-
carbon component. It is thought that that in order to produce hydrogen, there is a need to circulate the liquid to
remove the carbon particles being generated and to use a
pressure reduction device with an even higher exhaust
volume in order to increase energy efficiency. When Pnet
is used for P in Eq. (4), the ratio becomes as high as
113.5% (Pnet = 220.1W), exceeding that of the electrolysis
of water.
In contrast, when the actual consumed power standard Pall
is used, it becomes 50.8% (Pall=493W) of electrolysis.
Approximately 27 kJ/mole of enthalpy is required to create 1 mole of hydrogen from n-dodecane. The hydrogen
created from a hydrocarbon liquid uses approximately
10% of the theoretical amount of energy needed to create
it from the same amount of water. However, at most, only
39.4% of the Pnet is used for the chemical reaction. How
to optimize the composition of the device to prevent the
dispersion of heat and other factors, improving the value
of ε in Eq. (4) and improving the overall efficiency of the
system will be major issues in the future.
Fig. 2 Low-pressure plasma decomposition device
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
4. Experiments using a curve-shaped antenna
Experiments were conducted into the shape of the electrode in order to efficiently generate plasma in the microwave oven. As an improvement, the six antenna rods
arranged in a circle on the antenna unit shown in Fig. 3
were bent towards the center in the shape of a curve in
order to make the distance between the tips of the electrodes narrower. Making the distance between the tips of
the electrodes narrower would increase the strength of the
electrical field. The highest gas generation was obtained
when L=21 mm and d=10 mm.
Fig. 4 provides a comparison of the measured gas generation rates of the vertical antenna unit and the
curve-shaped antenna unit. The generation speed of the
gas was approximately up to 1.2 times greater with the
curved electrodes. While the reason for this cannot be
confirmed at this time, with the curve-shaped antenna, the
tips of the electrodes are close to each other and it appears
that the generation of plasma usually occurs near the center of the antenna, which makes the volume of the generated plasma larger.
Table II shows an analysis of the results of the gas
generated by each output. While there is little difference
in the ratio of hydrogen when compared with the straight
upright antenna, the gas generation rate, ε and η with curvature antenna are larger than that with was straight type.
On the other hand, the enthalpy of formation increased
under all test conditions when compared with the straight
upright antenna. This is because the ratio of acetylene
increased. The standard enthalpy of formation of acetylene is 227kJ/mole, which is high in comparison to others,
so there is a need to find reaction conditions that suppress
the formation of acetylene.
ted by the in-liquid plasma method is nearly the same as
the system shown in Fig. 1. However, all gases resulting
from the plasma decomposition underwent liquefied separation by passing through a liquid nitrogen trap, which
enabled hydrogen that was 97 to 99% pure to be collected.
Once the hydrogen has been stored in the hydrogen
storage tank by the downward displacement of water
method, it is absorbed into hydrogen storage alloys(rare
earth metals adjusted so that the LmNi type lanthanum
component is rich). For the verification test, approximately 150ml of waste engine oil or cooking oil was
placed in a microwave oven and broken down. Approximately 200 liters of hydrogen were extracted and used to
fuel a hydrogen-powered rotary engine. As a result, the
hydrogen-powered automobile could be propelled at 10
km/h for approximately 360 m.
If this technology were to be developed as a technology
for the decomposition of garbage or biomass materials, it
may be possible to realize a clean-operating hydrogen
vehicle that uses waste oil or garbage to produce its fuel.
Also, using this technology would enable hydrogen to be
collected from methane-hydride in the sea bed [2].
5. Experiments with hydrogen powered vehicle
The microwave oven device shown in Fig. 1 used
in-liquid plasma technology to decompose the material in
hydrogen that was collected and used in an experiment to
operate a Matsuda RX-8 Hydrogen RE hydrogen-powered
automobile. The system used to collect the hydrogen crea-
Fig. 4 Comparison of the amount of gas generated
40
v (mL/s)
30
20
10
0
70
Curvature type
Vertical type
80
90
E(V)
100
110
Fig. 5 Experiment with an internal hydrogen combustion
engine vehicle (Matsuda RX-8 Hydrogen RE)
References
(a)
(b)
Fig. 3 Overview of antenna unit: (a) Vertical Type,
L=22mm, (b) curved-shaped type, L=21mm.
[1]
Shinfuku Nomura, Hiromich Toyota, et al J. Appl. Phys.
106, 073306 (2009).
[2] Andi Erwin Eka Putra, Shinfuku Nomura, et al, Int. J.
Hydrogen Energy, 37, 16000-16005 (2012).