Investigation of hydrocarbon generation mechanism by polarizing the carboxy-group of fatty acid salt with microwave radiation

Article abstract of DOI:10.14233/ajchem.2014.15402

Triglycerides can be converted to renewable hydrocarbons fuel which can be used as engine fuels by alkali pyrolysis decarboxylation and cracking processes. The purpose of present study was to explore decarboxylation mechanism of fatty acid salt with microwave radiation. Sodium stearate, potassium stearate, sodium oleate and sodium laurate was chosen as a model compound. The carboxy-terminal of this dipolar molecule was further polarized with microwave radiation. The Lorentz force of ions of dipolar molecules were moved in accordance with the way of electromagnetic waves, contribute to the formation of carbanion, which effectively promote the decarboxylation reaction. Moreover, the polarity of carboxy-terminal was stronger, more easily decarboxylation. The surface of glycerol formed a High-Temperature Locus in microwave radiation reaction system, facilitate the decarboxylation processe, in adition to played a role as the hydrogen donor for this high dielectric value compound. C8-C20 n-alkanes and n-alk-1-enes were arranged regular in liquid products. It proved the feasibility to derive renewable hydrocarbon fuel from sodium salt of fatty acids by microwave pyrolysis.

Full text of DOI:10.14233/ajchem.2014.15402

Asian Journal of Chemistry; Vol. 26, No. 2 (2014), 369-375
http://dx.doi.org/10.14233/ajchem.2014.15402
Investigation of Hydrocarbon Generation Mechanism by Polarizing the
Carboxy-group of Fatty Acid Salt with Microwave Radiation
1
,2
1,2,*
1,2
1,2
1,2
1,2
Y.P. WANG , Y.H. LIU , R. RUAN , P.W. WEN , Y.Q. WAN and J.S. ZHANG
1
Engineering Research Center for Biomass Conversion, Nanchang University, 235 Nanjing Road, Nanchang City 330047, Jiangxi Province, P.R. China
2
State Key Laboratory of Food Science and Technology, 235 Nanjing Road, Nanchang City 330047, Jiangxi Province, P.R. China
Corresponding author: Tel/Fax: +86 791 88333281; Email: liuyuhuan@ncu.edu.cn
Received: 1 March 2013; Accepted: 29 May 2013; Published online: 15 January 2014;
*
AJC-14545
Triglycerides can be converted to renewable hydrocarbons fuel which can be used as engine fuels by alkali pyrolysis decarboxylation and
cracking processes. The purpose of present study was to explore decarboxylation mechanism of fatty acid salt with microwave radiation.
Sodium stearate, potassium stearate, sodium oleate and sodium laurate was chosen as a model compound. The carboxy-terminal of this
dipolar molecule was further polarized with microwave radiation. The Lorentz force of ions of dipolar molecules were moved in accordance
with the way of electromagnetic waves, contribute to the formation of carbanion, which effectively promote the decarboxylation reaction.
Moreover, the polarity of carboxy-terminal was stronger, more easily decarboxylation. The surface of glycerol formed a “High-Temperature
Locus” in microwave radiation reaction system, facilitate the decarboxylation processe, in adition to played a role as the hydrogen donor
for this high dielectric value compound. C8-C20 n-alkanes and n-alk-1-enes were arranged regular in liquid products. It proved the
feasibility to derive renewable hydrocarbon fuel from sodium salt of fatty acids by microwave pyrolysis
Keywords: Microwave radiation, Fatty acid salt, Decarboxylation, Hydrocarbon.
solved, for instance, large temperature gradient, slow heating
7, 8
rate and non-selective decarboxylation .
INTRODUCTION
Lack of fossil fuels has been a serious threat to the world's
energy and economic security, so the popularity of alternative
energy and interest in the development of renewable fuels and
chemicals are rapidly increasing. On the demand side, interest
has been gradually changed to the research of high heat value
fuels such as aviation gasoline and kerosene.
Pyrolysis of the whole triglyceride has been shown to result
,10
9
in oxygenated products
through complex free-radical
11
reactions . There are little work on the pyrolysis of fatty acid
salt, which can be released from triglycerides through various
saponification techniques. Many researchers have considered
the deoxygenation of fatty acids using different catalysts.
However, there are no detailed studies involving the decar-
boxylation or deoxygenation of fatty acids solely by thermal
means. SBA-15/Pd and Pd/C was used to catalyze the decar-
People produced biodiesel by transesterification or by
pyrolysis method. The main process is the conversion of vege-
1
table oil to diesel . But economic factors and the nature of
biodiesel limits its development. For example, the flow of
biodiesel is poor at low temperature not suitable for use in
cold areas. The molecular structure of functional groups
containing oxygen, compared with diesel, its calorific value
is lower by 9-13 %. In addition, the thermal stability of biodiesel
1
2,13
boxylation or deoxygenation of fatty acids , although
obtained high-quality hydrocarbon. But it is subject to multiple
conditions that can not to be applied. The most recent study
examined liquid-phase pyrolysis of stearic acid (C18
H
36
O
2
) in
dodecane using Pd/C catalysts . The main product was n-
heptadecane and CO was identified in the gas phase, making
14
2,3
is relatively poor, prone to deterioration and oxidation . It
has caused all scholars interest through the pyrolysis of fatty
acid to obtain high purity of hydrocarbons. But thermochemical
pyrolysis reaction was not easy to control, heating at a slower
speed, poor selectivityand existence of many side reactions
Microwave heating has been developed rapidly in recent years,
which may preferentially activate the polar partial of the long
chain molecule, leading to the high selectivity of decarboxy-
2
it likely that the initial reaction is decarboxylation of the fatty
acid. The deoxygenated hydrocarbon chain produced through
the decarboxylation of fatty acids could be processed further
to yield shorter-chain hydrocarbons that could potentially be
used as petrochemical replacements. Mechanisms involving
thermal decomposition of fatty acids after initia decarboxylation
have not been reported.
4
-6
lation . Shortcomings of the traditional heating has been

370 Wang et al.
Asian J. Chem.
The main products of stearic acid pyrolysis was series
of n-alkanes and n-alk-1-enes and some undesired oxy-
compound. It is associated with the traditional heating that
liquids were concentrated using a vacuum rotary evaporator
(EYELA WATER BATH SB-2000) to a near constant weight
and the weight was recorded. The viscosity and density of the
collected liquid were determined (SYD-265B and DM-100).
The weight of gas product was calculated using the following
equation:
15, 16
had not strong selectivity . Microwave radiation that can
change order and the bonding strength of the chemical bonds
of polarity molecules, transform fatty acid into fatty acid salt
by saponification, which can increase the polarity of carboxyl
terminal, using microwave heating technology, which may
preferentially activate the polar molecule and functional groups
of the fatty acid salt molecular, leading to the high selectivity
of decarboxylation.This research mainly study the decarboxy-
lation and cyclization mechanism of different metal salts of
fatty acids, different saturation and length of carbon chain fatty
acid salt in the condition of microwave radiation. Sodium
stearate, potassium stearate, sodium oleate and sodium laurate
were chosen as a model compound, glycerol played a role as
the hydrogen donor and microwave absorber for this high
dielectric value compound. It was shown that n-alkanes and
n-alk-1-enes had overwhelming superiority by qualitative and
semi-quantitative analysis in pyrolysis product, proofed unique
advantages that microwave pyrolysis fatty acid salt decarboxy-
lation into the hydrocarbon. Moreover, different fatty acid salt
were compared. It was proved that it is feasible to derive rene-
wable hydrocarbon fuel from natural triglyceride by micro-
wave pyrolysis.
Weight of gas = Initial samples – Pyrolytic liquid mass –
Char residue mass
Detection method: Chemical compositions of the liquid
products were analyzed using an Agilent 6890N/5973 innet
gas chromatography/mass spectrometer (Santa Clara, CA) with
a HP-5ms capillary column. The GC was programmed at 60 °C
for 2 min and then increased at 10 °C/min to 280 °C and finally
held with an isothermal for 10 min. The injection temperature
was 280 °C and the injection size was 0.2µl. The flow rate of
the carrier gas (helium) was 1 mL/min. The ion source tempe-
rature was 230 °C for the mass selective detector.The compounds
were identified by comparison with the NIST Mass Spectral
Database. Only quality matches of above 85 % were recorded.
All experiments were performed in quintuplicate. The data
presented in this paper are averaged values. Statistical analysis
of the data was conducted using origin 8.0. The standard
deviations are presented along with the fractional yield data.
RESULTS AND DISCUSSION
Decarboxylation of sodium stearate under different
microwave power and glycerol content: The content of
sodium stearate pyrolytic products under different microwave
power levels are different as shown in Fig. 1. The content of
liquid hydrocarbon is increased with the increase of power,
but slight changes (in average 50 to 57 %) take place and the
amount of liquid ranged from 63 to 70 %.
EXPERIMENTAL
Sodium stearate, potassium stearate, sodium oleate and
sodium laurate were purchased from Sinopharm Chemical
Reagent Co. Ltd in Chinese with > 99 % purity. Others were
analytical reagents made in China. Microwave pyrolysis
apparatus was manufactured by SinEo in Shanghai. This
apparatus is designed by our team.Agilent 6890N/5973 innet
GC-MS (Agilent Technologies); Chromatographic column
(
HP-5 ms, 30 m × 0.25 mm × 0.25 µm); FT-IR Nicolet 5700
Thermo Nicolet Corporation); GC 9310 (Chromatography
Charcoal
(
Instrument Co., Ltd. Shanghai).
Hydrocarbon
60
40
20
0
Heavy oil
Synagas
General procedure
Pyrolysis device is composed of microwave generators,
reactor, condensing system, connecting tubes and liquid
collection bottle. The pyrolysis of samples was carried out in
a Sinko Bench type Microwave Oven by placing 30 g prepared
samples (sodium stearate; potassium stearate; sodium oleate;
sodium laurate) mixed with 10 % glycerol (wt. %) in a quartz
flask, which in turn was placed inside the cavity of micro-
wave. Oven is supplied with infrared probe to control tempe-
rature. Condensing system was composed of condense liquid
collecting bottle and series condenser pipe, opening condensed
circulatory system until the temperature of condensed water
is below 3 °C. The time for microwave treatment was around
400
600
Power(W)
800
Fig. 1. Decarboxylation of sodium stearate product fractional yields in
different microwave radiation (10 min)
1
0 min. A constant power input of 400 W, 600 W, 800 W was
The main products of sodium stearate pyrolysis were
n-alkanes and n-alk-1-enes and cyclic hydrocarbons. The peak
area of each product can be determined semi-quantitative
through the standard of known concentration in the computer.
As shown in Fig. 2 and Table-1, n-alkanes and n-alk-1-enes
used for each batch, using infrared probe to record the change
of temperature. The fraction collected from the bottles connected
on the bottom of the condensers is pyrolytic liquid.
The solid char residue was allowed to be cooled down to
the room temperature before it was weighed. The condensates
adhering to the interior wall of the quartz flask were washed
with ethanol into the pyrolytic liquid collection bottle. Collected
8
series were arranged from C to C20 regularly, which is in line
with the law of hydrocarbon pyrolysis; diene series was also

Vol. 26, No. 2 (2014)
Hydrocarbon Generation Mechanism by Polarizing the Carboxy-group of Fatty Acid Salt 371
TABLE-1
MAIN COMPONENTS AND RELATIVE CONTENTS OF LIQUID PRODUCTS BY MICROWAVE
PYROLYSIS OF SODIUM STEARATE AT DIFFERENT POWERS
Retention time (min)
600W
Relative content (%)
600W
a
M
400W
0 %
glycerol glycerol glycerol glycerol glycerol glycerol glycerol glycerol glycerol glycerol
800W
10 %
400W
10 %
800W
10 %
Type
Hydrocarbon
1
5 %
10 %
20 %
5 %
10 %
20 %
Octenes
112
168
3.26
9.78
3.25
9.76
3.26
9.75
3.25
9.77
3.26
9.77
1.04
3.62
4.61
6.47
8.75
5.07
6.72
1.72
0.56
0.63
0.35
0.12
0.09
0.33
-
1.00
3.94
4.88
7.55
10.26
5.41
7.31
1.23
0.43
0.32
0.59
1.21
3.93
4.27
7.13
9.79
5.39
7.27
1.44
0.48
0.48
0.32
0.13
0.08
0.40
0.10
-
0.98
4.17
4.80
7.53
10.36
5.51
7.40
1.41
1.08
3.68
4.67
6.84
9.39
5.03
6.83
1.24
0.41
0.30
0.69
0.12
0.10
0.38
0.08
-
Dodecenes
Tridecenes
Tetradecenes
Pentadecenes
182 11.27
196 12.74
210 14.09
224 15.23
238 16.45
252 17.37
11.26
12.72
14.09
15.21
16.42
17.37
18.40
19.26
21.70
11.23
12.69
14.06
15.18
16.40
17.35
18.40
19.26
21.70
3.73
11.26
12.72
14.10
15.21
16.43
17.37
11.26
12.71
14.08
15.21
16.42
17.36
18.40
19.26
21.70
3.72
Alkenes Hexadecenes
Heptadecenes
Octadecenes
1
8.41
9.26
Nonadecenes
Eicosylenes
266
18.41
0.43
1
280 21.71
.73
21.71
3.72
5.53
4.56
7.01
-
0.37
0.09
0.17
0.37
0.09
-
3
Methylcycloheptene 110
3.72
0.10
Ring-
containing Cycloheptene
alkenes
5.54
4.56
-
5.54
5.53
96
4.56
-
4.56
4.56
0.32
-
Cyclodecene
138
7.01
7.01
Cyclododecene
166 13.06
110 4.24
-
-
-
0.09
0.03
0.15
0.17
0.26
0.16
0.30
0.31
1.00
1.60
1.73
1.40
1.55
1.25
0.12
0.24
0.48
0.32
0.56
-
1
1
1
,4-Octadiene
-
-
-
-
-
-
-
-
,11-Dodecadiene
,12-Tridecadiene
166 13.63
180 14.37
13.62
14.35
14.90
15.51
16.10
16.68
3.36
4.89
6.62
8.31
9.88
13.61
14.34
14.89
15.50
16.08
16.67
3.36
13.62
14.36
14.90
15.52
16.10
16.68
3.36
4.89
6.62
8.31
9.89
11.41
11.52
12.89
14.25
15.39
16.57
13.62
14.35
14.90
15.52
16.09
16.68
3.36
0.13
0.20
0.17
0.08
0.21
0.18
0.88
1.49
1.72
1.68
1.60
0.14
0.22
0.19
0.10
0.26
0.23
1.10
1.80
2.01
1.82
1.93
0.13
0.21
0.17
0.09
0.19
0.18
0.88
1.45
1.84
1.93
1.85
2.01
0.04
0.20
0.37
0.24
0.40
0.12
0.21
0.15
0.09
0.19
0.23
0.95
1.65
1.83
1.61
1.50
Dienes
1,13-Tetradecadiene 194 14.91
1,14-Pentadecadiene 208 15.52
1,15-Hexadecadiene 222 16.10
1,16-Heptadecadiene 236 16.69
Octanes
114
128
142
156
170
3.37
4.91
6.64
8.33
9.90
11.42
Nonanes
Decanes
4.90
4.90
6.62
6.63
Undecanes
Dodecanes
8.30
8.31
9.87
9.88
Alkanes
Tridecanes
184
11.40
11.38
11.40
1.81
2.59
1.99
11.53
Tetradecanes
Pentadecane
Hexadecane
Heptadecane
198 12.90
212 14.27
226 15.40
240 16.59
12.89
14.25
15.39
16.57
12.88
14.22
15.37
16.56
3.86
12.89
14.25
15.38
16.57
3.86
0.19
0.41
0.19
0.40
0.08
0.09
0.07
1.71
0.16
0.19
0.43
0.23
0.50
0.10
0.12
0.10
2.00
0.23
0.18
0.41
0.19
0.43
0.09
0.12
0.09
1.87
0.21
3
.86
4.12
.40
3
.86
.12
0.09
0.06
Ethyl cyclohexane,
112
4.12
4.40
3.86
4.12
4.40
0.08
4
4
Ring-
containing
alkanes
Hexyl cyclopropane 126
Proyl cyclohexane 126
,2-Dimethyl
4.76
5.08
4.75
5.07
4.76
4.75
5.03
4.76
1.74
0.20
1.69
0.31
5.08
5.08
1
1
40
6.48
8.19
6.48
8.17
6.47
8.16
6.47
8.17
6.48
8.17
2.83
3.03
2.88
3.45
3.29
3.32
2.99
3.71
3.12
3.34
cyclooctane
Pentyl cyclohexane
154
a
Relative molecular mass.
o
n-alk-1-enes
n-alkanes
Ring-containing alkanes
1
5
16
o
17
o
Pentadecene and heptadecene content were the most
important in pyrolysis products, others have a slight difference
of peak area in different carbon atoms in the same series of
hydrocarbons, compared with the traditional pyrolysis products,
7
14
o
x
r
8
6
4
2
.0x10
o
1
2
13
o
x
1
1
7
10
r
r
o
.0x10
8
o
9
r
x
x
x
Octadecanoic acid, ethenyl ester
x
7
x
x
.0x10
18
x
o
x
7
x
.0x10
x
0
.0
17
which was concerned possibly with microwave radiation .
Medium compounds mainly happened while the dipole turning-
direction polarization and interface polarization in the micro-
5
10
15 20
Retention time (min)
25
30
35
Fig. 2. Main products formed in the microwave pyrolysis experiments
600W and 10 min) on sodium stearate
(
1
8,19
wave field . Depending on C-terminus's polarity was the
biggest in the long chain fatty acid salt and dipole made
desultorily movement and arrangement.
observed a slight variation, from C12 to C17 respectively. The
pyrolysis gas of a semi-quantitative analysis of gas phase
showed that the existence of CH and proved that the sodium
The C-terminus's dipole arranged again and positive
charge moved to the negative electrode trend when micro-
wave played role in the polarity along with the change of the
4
stearate long-chain hydrocarbon of free fracture happened
again after the formation of long-chain hydrocarbon.

372 Wang et al.
Asian J. Chem.
microwave. Lorentz force of ion or polarity molecules forced
to move according to the electromagnetic wave function way,
which leads to reduce the entropy and molecule collision risk
effectively increases billions of times contrast with no catalytic
TABLE-2
MAIN COMPONENTS OF GAS PRODUCTS BY
MICROWAVE PYROLYSIS OF SODIUM STEARATE
Power
400 W
CO (%)
2
CO (%)
34.94
33.18
34.87
CH (%)
4
C (%)
2+
H (%)
2
20, 21
46.12
45.63
39.26
1.45
1.69
1.82
2.41
2.03
2.45
15.08
17.47
21.60
microwave's . In addition, the glycerol (hydrogen donor)
was strong microwave absorbing agent added in the reaction
system because its dielectric constant is 56.2. Fatty acid salt is
strongly activated near glycerin interface leading to decarboxy-
lation reaction. Hydrocarbon products quickly deviate from
high-temperature zone. Based on the above analyses, we can
infer the possible decarboxylation mechanism of sodium
stearate as shown in Fig. 3 in the action of microwave and
glycerol.
6
00 W
00 W
8
microwave; Glycerin
O
ONa
+
CO2
microwave
O
+
ONa
+
CO + H O
2
O
Fig. 4. Decarboxylation pathway of sodium stearate in microwave radiation
-
O
22
the specific mechanism has not been proved . It was sure that
naphthenic hydrocarbons, helpful for hydrocarbon fuel
preservation, are more stable than n-alk-1-enes in pyrolysis.
The content of n-alk-1-enes, n-alkanes and naphthenic
hydrocarbon is increased with the increase of microwave
power,while the dienes and oxygen compounds are gradually
reduced. A lot of octadecanoic acid ethenyl ester found in
microwave assisted pyrolysis productst are not found in tradi-
-
OH
Na
-
-
C
O
O
C
O +C17H33
C16H31
C
-
O
-
O Na
-
+
O Na
-
H
+
Na
O
C
O
C
C17H34
23
+
C17
-
+
+
tional pyrolysis previously mentioned . This is due to the
33
OH
O Na
addition of glycerol which play an important role in reducing
the activation energy as high-temperature locus in decarboxy-
lation reaction, assumed hydrogen donor in the system.
Glycerol and sodium stearate would also enhancing complex
esterification. As the amount of glycerol is increased, octade-
canoic acid and ethenyl ester are also regularly increased
microwave pyrolysis
C ~C n-alk-1-enes;
8
17
n-alkanes, etc.
Fig. 3. Decarboxylation reaction mechanism of sodium stearate in
microwave radiation
(
Table-3).
Decarboxylation of fatty acid salt for different metal
The carboxy-terminal's positive and negative ion migra-
tory direction of sodium stearate formed orderly arrangement
under the microwave field, leading to a reduction of activation
energy. Carbanion formed under fierce collision with glycerol
surface of high-temperature locus under variable microwave
frequency, which was relatively stable. The same series of n-
alk-1-enes and n-alkanes were obtained after sodium stearate
decarboxylation at relatively stable microwave field. FI-IT
showed that large amounts of solid sodium carbonate con-
tained in solid the after pyrolysis, which proved the correctness
of the reasoning process. Two reactions may occurred during
decarboxylation process, long-chain hydrocarbons were
fractured to produce different carbon chain length of n-alk-1-
enes and n-alkanes under high temperature, accompanied by
methane, ethane, ethylene and acetylene gases (Fig. 4 and
Table-2).
salts, different saturation and different carbon chain
length: The microwave pyrolysis product distribution of
sodium stearate, potassium stearate, sodium oleate and sodium
laurate are shown in Fig. 5. The yield of sodium oleate liquid
hydrocarbons was the highest, while the yield of heavy oil
(
wax) is zero. Under the conditions of microwave and because
of the existence of sodium oleic double bond there may be an
enhancement of the reaction activity in some areas of carbon
chains. Double bonds can reduce the pyrolysis energy barrier
of the proximate C-C single bonds and made β C-C fracture
occupying the leading position and make it difficult to form
long-chain wax. The probability of short-chain fatty acid salt
got polymerized to form long-chain wax was also very small.
As sodium stearate, the major product of potassium stearate;
sodium oleate and sodium laurate pyrolysis was also n-alkanes,
9
C -C11 n-alk-1-enes was not found in microwave assisted
8
n-alk-1-enes and cyclic hydrocarbons, from C to C20. Sodium
pyrolysis products, but generating same series naphthenic
hydrocarbon with the side chain. This is different from tradi-
tional pyrolysis. This was also consistent with the microwave
cyclization reaction mentioned in the relevant article. However,
stearate, potassium stearate and sodium laurate pyrolysis
arranged regularly, but the product of sodium oleate pyrolysis
was arranged complex. A large number of cycloolefin and
cycloparaffins were produced in the product of sodium oleate

Vol. 26, No. 2 (2014)
Hydrocarbon Generation Mechanism by Polarizing the Carboxy-group of Fatty Acid Salt 373
TABLE-3
RELATIVE CONTENTS OF VARIOUS HYDROCARBONS IN LIQUID PRODUCTS FORMED FROM
MICROWAVE PYROLYSIS OF SODIUM STEARATE UNDER DIFFERENT GLYCEROL CONTENT
4
00 W
600 W
800 W
Type
1
0 % glycerol (%)
5 % glycerol (%)
3.37
10 % glycerol (%)
20 % glycerol (%)
10 % glycerol (%)
C –C hydrocarbons
9
3.64
38.5
0.63
7.65
7.95
1.38
4.65
7.58
28.02
4.11
40.50
0.71
9.70
9.16
1.14
4.37
4.01
26.30
3.31
41.98
0.72
8.88
8.78
0.97
4.45
4.69
26.22
3.68
39.08
0.68
8.14
8.84
0.99
4.14
4.19
30.26
3
C -C alkenes
1
41.92
0.42
0
20
Ring-containing alkenes
C -C alkanes
8.00
1
0
17
Ring-containing alkanes
Dienes
8.44
0.97
Octadecanoic acid, ethenyl ester
Other oxygen-containing
Others (unidentified)
4.21
4.04
28.63
TABLE-4
MAIN COMPONENTS AND RELATIVE CONTENTS OF LIQUID PRODUCTS BY MICROWAVE
PYROLYSIS FOR DIFFERENT SODIUM SALTS OF FATTY ACID
Retention time (min)
Relative content (%)
a
Type
Hydrocarbon
Octenes
M
Sodium Potassium Sodium
stearate
Sodium
laurate
Sodium
stearate
Sodium
stearate
Sodium
oleate
Sodium
laurate
stearate
oleate
112
126
Nonenes
-
-
-
-
4.95
-
-
-
-
0.44
1.81
0.74
0.36
2.06
1.49
0.79
0.50
-
-
6
.44
Decenes
140
6.66
6.69
0.27
6
8
8
.79
.37
.49
Undecenes
Dodecenes
Tridecenes
154
168
182
-
8.45
8.39
-
0.15
14.28
0.46
9
.74
9.88
4.03
0.15
9.75
11.23
9.85
3.93
4.27
10.01
10.01
Alkenes
11.12
1.27
0.57
1.26
10.12
3.47
0.16
0.37
2.14
2.44
-
11.24
11.20
5.23
2.96
11.30
Tetradecenes
Pentadecenes
Hexadecenes
Heptadecenes
Octadecenes
196
210
224
238
252
12.69
14.06
15.18
16.40
17.35
12.67
14.13
15.18
16.40
17.36
18.57
19.21
-
12.56
13.90
0
12.54
14.16
15.14
16.42
17.37
18.26
19.26
-
7.13
9.79
5.39
7.27
1.44
0.48
0.48
0.32
7.70
15.25
5.73
11.53
1.39
3.58
0.37
-
3.17
4.64
0
16.31
17.23
18.27
19.26
-
1.75
2.03
1.29
0.76
-
1
8.40
9.26
Nonadecenes
266
280
110
1
Eicosylenes
21.70
3
5
.73
.54
0.13
0.08
0.40
-
Methylcycloheptene
5.52
3.71
3.71
0.07
0.39
0.06
cycloheptene
96
4.56
4.55
-
4.54
0.28
-
0.22
Propyl cyclopentene
Propenyl cyclopentene
110
108
-
-
-
-
4.03
5.08
-
-
-
-
0.11
0.33
0.57
0.64
0.48
0.47
0.73
1.58
1.73
0.75
1.74
0.41
0.79
0.67
0.89
3.12
3.87
1.29
2.59
0.72
0.51
-
-
-
-
5
5
.30
.70
Butyl cyclopentenes
124
-
-
-
-
-
-
Propyl cyclohexene
Cyclodecene
124
138
-
-
-
5.90
6.87
7.48
7.61
8.70
-
-
-
-
-
-
-
7.01
0.10
Ring-
containing
alkenes
Butyl cyclohexene
138
-
-
-
-
-
-
Pentyl cyclohexene
Cycloundecene
152
152
166
-
-
-
-
-
-
8.71
10.17
-
-
-
-
-
-
-
0.37
0.20
-
8
.90
10.23
10.37
10.47
12.05
Hexyl cyclohexene
12.07
12.26
13.38
-
0.39
0.31
0.43
-
Octyl cyclopentene
180
-
-
12.23
3.42
-
-
1
Cyclododecene
166
222
166
180
194
208
222
236
-
-
14.94
15.52
10.74
11.65
12.38
-
-
-
Decyl cyclohexene
-
-
-
-
-
0
-
1,11-Dodecadiene
1,12-Tridecadiene
1,13-Tetradecadiene
1,14-Pentadecadiene
1,15-Hexadecadiene
1,16-Heptadecadiene
13.61
14.34
14.89
15.50
16.08
16.67
0
14.36
14.89
-
13.58
14.28
14.86
-
0.14
0.22
0.19
0.10
0.26
0.23
0.53
0.53
0.41
-
0.12
0.12
-
Dienes
16.07
-
16.15
16.41
16.11
16.73
0.18
-
7.43
1.30
3.29
0.64

374 Wang et al.
Asian J. Chem.
Octanes
114
128
142
156
170
3.36
4.90
6.62
8.30
9.87
3.36
4.88
6.60
8.29
9.85
11.38
3.35
4.86
6.56
-
3.35
4.94
6.64
8.55
9.99
11.44
11.60
12.96
0
1.10
1.80
2.01
1.82
1.93
0.84
1.54
1.56
2.06
1.77
2.72
0.35
0.26
0.86
0.34
1.01
0.82
0.93
3.42
0.62
0.48
0.34
0.44
0.46
0.30
-
Nonanes
0.98
0.61
-
Decanes
Undecanes
Dodecanes
-
-
Alkanes
11.28
11.52
12.91
-
1.22
0.36
0.40
0
Tridecanes
184
11.38
2.59
11.50
Tetradecanes
Pentadecane
Hexadecane
Heptadecane
198
212
226
240
12.88
14.22
15.37
16.56
12.86
14.28
15.37
16.62
0.19
0.43
0.23
0.50
-
0
-
16.52
-
-
0.50
0.35
0.49
1.26
0.16
0.11
0.27
0.40
-
-
3
4
.86
.51
Ethyl cyclohexane
Hexyl cyclopropane
112
126
3.86
4.76
3.85
4.73
0.10
2.00
0.06
1.64
-
4.73
.12
4.24
.40
4.75
2.36
4
4
4
.12
.40
0.12
0.10
Ethylidene cyclohexane
110
4.11
-
0.08
-
4
Ring-
containing Propenyl cyclohexane
126
140
154
154
5.08
6.47
8.16
-
-
5.44
-
-
0.23
3.29
3.32
-
-
-
alkanes
1,2-Dimethyl cyclooctane
Pentyl cyclohexane
Cyclododecane
6.45
8.15
-
6.57
-
2.71
3.69
-
7.09
-
8.14
9.72
3.08
3.15
1.17
2.46
2.78
9.72
1.84
14.34
Nonyl cyclohexane
Cyclohexadecane
210
224
-
-
-
-
-
-
-
-
-
-
14.68
15.11
16.86
0.17
a
Relative molecular mass
8
11
10
o
x
r
n
-alk-1-enes
Charcoal
1.0x10
15
o
7
r
o
16
n-alkanes
Hydrocarbon
Heavy oil
Synagas
8.0x10
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
7
8
o
9
r x
o
17
o
Ring-containing alkanes
6.0x10
1
4
7
x
12
o
x
x
4.0x10
x
1
3
o
x
18
7
x
o
x
x
x
o
x
2
.0x10
0.0
5
10
15 20
Retention time (min)
25
30
35
Fig. 8. Main products formed in the microwave pyrolysis experiments
(600W and 10 min) onlaurate sodium
the atomic radius and polarity are larger than that of sodium,
the carboxy-terminal of this dipolar moleacule is further
polarized with microwave radiation. The Lorentz force of ions
of dipolar molecules are moved in accordance with the way
of electromagnetic waves leading to the formation of carbanion
which is effectively promote the decarboxylation reaction.
Moreover, the polarity of carboxy-terminal is stronger resulting
in more easily decarboxylation. The decarboxylation mechanism
of fatty acid salt is proved to be correct by another way in
microwave radiation. Dienes content are the most important
in pyrolysis products of sodium oleate. The double bonds are
more hard to be cracked than the single bonds during pyrolysis
decomposition. Thus, sodium oleate double bonds are kept in
the liquid final product. At the same time, the existence of
double bonds promoted the presence of cyclization reaction.
Sodium stearate Potassium stearate Sodium oleate Laurate sodium
Fig. 5. Product yields (%) for different sodium salts of fatty acid (600 W
and 10 min)
during microwave assisted pyrolysis, which may be due to
microwave radiation accelerated cyclization reaction for
24, 25
compounds containing double bond
(Figs. 6-8, Table-4).
1
5
17
o
8
7
7
7
7
14
o
1
8
6
4
2
.0x10
.0x10
.0x10
.0x10
.0x10
o
16
o
o
x
r
n
n
-alk-1-enes
-alkanes
12
o
13
ox
11
r
1
0
Ring-containing alkanes
8
o
9
r
r
x
x
x
x
Octadecanoic acid, ethenyl ester
x
x
18
o
x
x
x
x
0
.0
5
10
15
20
25
30
35
Retention time (min)
Fig. 6. Main products formed in the microwave pyrolysis experiments
600W and 10 min) on potassium stearate
(
C
13-C19 n-alkanes and n-alk-1-enes are found in pyrolysis
products of laurate sodium (C12), due to polymerization.
However, the reaction intensity is small (Table-5).
7
8
6
4
2
.0x10
7
.0x10
7
.0x10
Conclusion
7
.0x10
The purpose of present study was to explore decarboxy-
lation mechanism of fatty acid salt with microwave radiation.
Sodium stearate, potassium stearate, sodium oleate and
sodium laurate was chosen as a model compound, which proved
the feasibility to produce high quality renewable hydrocarbon
fuel with fatty acid salt by microwave assisted pyrolysis. The
following conclusions were obtained: (a) It is feasible to
produce high quality renewable hydrocarbon fuel using fatty
0
.0
5
10
15
Retention time (min)
20
25
30
35
Fig. 7. Main products formed in the microwave pyrolysis experiments
600W and 10 min) on sodium oleate
(
In addition, the peak area of C15-C17 n-alkanes and n-alk-
-enes are larger than other three materials. Because the
1
carboxyl terminal of potassium stearate was kalium, for which

Vol. 26, No. 2 (2014)
Hydrocarbon Generation Mechanism by Polarizing the Carboxy-group of Fatty Acid Salt 375
TABLE-5
RELATIVE CONTENTS OF VARIOUS HYDROCARBONS IN LIQUID PRODUCTS FORMED FROM
MICROWAVE PYROLYSIS FOR DIFFERENT SODIUM SALTS OF FATTY ACID
Type
Sodium stearate (%)
Potassium stearate (%)
Sodium oleate (%)
Sodium laurate (%)
C -C hydrocarbons
3
4.11
40.50
0.71
9.70
9.16
1.14
4.37
4.01
26.30
3.39
55.38
0.35
2.99
24.35
20.56
3.09
15.68
12.55
0
5.88
36.54
1.98
2.64
11.46
5.40
0
9
C -C alkenes
20
10
Ring-containing alkenes
C -C alkanes
10.93
8.18
10
17
Ring-containing alkanes
Dienes
0.42
Octadecanoic acid, ethenyl ester
Other oxygen-containing products
Others (unidentified)
5.01
3.98
9.64
11.14
10.03
26.07
12.36
acid salt by microwave assisted pyrolysis. (b) The mechanism
of microwave promoting the fatty acid decarboxylation by
acting on the carboxyl terminal is proved. The carboxy-
terminal of this dipolar moleacule is further polarized with
microwave radiation. The Lorentz force of ions of dipolar mole-
cules are moved in accordance with the way of electromagnetic
waves, contribute to the formation of carbanion, which is
effectively promote the decarboxylation reaction. (c) In the
microwave field, as the carboxy-terminal polarity of potassium
stearate is the strongest, thus the decarboxylation is most
effective. The double bonds are more hard to be cracked than
the single bonds during pyrolysis decomposition. Therefore,
sodium oleate double bonds are kept in the liquid final product.
At the same time, the existence of double bonds promoted the
presence of cyclization reaction. (d) Glycerol surface formed
high-temperature locus in the reaction system under the
microwave field, which activated the reaction process as well
as a role for hydrogen donor. But too much glycerol would
lead to the formation of octadecanoic acid ethenyl ester.
Saponification waste oil produced fatty acid salt also have
glycerol as the by-productand some glycerol could be left in
the system as natural catalyst providing a feasible method to
produce high calorific value-hydrocarbon fuels by waste oil.
national Cooperation of Jiangxi Province (No. 20101208);
Internantional Science & Technology Cooperation Program
of China (No. 2010DFB63750); Natural Science Foundation
of Jiangxi Province (No. 2008GZH0047).
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of Jiangxi Province (GJJ13017), (SKLF-ZZB-201312). Inter-