Optimizing reaction conditions for the isomerization of fatty acids and fatty acid methyl esters to their branch chain products

Article abstract of DOI:10.1007/s11746-010-1718-3

In order to improve the oxidative stability and cold flow properties of oleic acid or methyl oleate, branch chain isomerization was conducted using a beta zeolite catalyst. Reaction conditions of temperature (200-300 °C), pressure (0.1-3.0 MPa), and co-catalyst (0-2 wt%) were optimized based on branch chain conversion and the cloud point of the ester following the isomerization reaction of oleic acid or methyl oleate. Fourier transform infrared spectroscopy (FTIR) and Gas Chromatograph equipped with Mass Spectrometry (GC/MS) analyses were used to analyze and quantify the isomerization product samples, while the cloud point of each sample was tested. The lowest and therefore, best cloud point measured was -15.2 °C at conditions of 200 °C, 3 MPa, and 2% co-catalyst using methyl oleate as a starting material. The highest branch chain conversion achieved was 50% under conditions of 300 °C, 1.5 MPa and 0% co-catalyst using oleic acid as a starting material. The use of oleic acid and methyl oleate is based on whether it is optimal to carry out the skeletal isomerization before or after the esterification reaction. Performing the isomerization reaction on the ester was preferred over the fatty acid based on the trans isomerization and cloud point results. Reducing the unbranched trans isomers was desirable in obtaining a low cloud point. AOCS 2010.

Full text of DOI:10.1007/s11746-010-1718-3

J Am Oil Chem Soc (2011) 88:661–671
DOI 10.1007/s11746-010-1718-3
ORIGINAL PAPER
Optimizing Reaction Conditions for the Isomerization
of Fatty Acids and Fatty Acid Methyl Esters to Their
Branch Chain Products
•
Stephen J. Reaume Naoko Ellis
Received: 29 March 2010 / Revised: 11 November 2010 / Accepted: 12 November 2010 / Published online: 1 December 2010
Ó AOCS 2010
Abstract In order to improve the oxidative stability and
cold flow properties of oleic acid or methyl oleate, branch
chain isomerization was conducted using a beta zeolite
catalyst. Reaction conditions of temperature (200–300 °C),
pressure (0.1–3.0 MPa), and co-catalyst (0–2 wt%) were
optimized based on branch chain conversion and the cloud
point of the ester following the isomerization reaction of
oleic acid or methyl oleate. Fourier transform infrared
spectroscopy (FTIR) and Gas Chromatograph equipped
with Mass Spectrometry (GC/MS) analyses were used to
analyze and quantify the isomerization product samples,
while the cloud point of each sample was tested. The
lowest and therefore, best cloud point measured was
-15.2 °C at conditions of 200 °C, 3 MPa, and 2%
co-catalyst using methyl oleate as a starting material. The
highest branch chain conversion achieved was 50% under
conditions of 300 °C, 1.5 MPa and 0% co-catalyst using
oleic acid as a starting material. The use of oleic acid and
methyl oleate is based on whether it is optimal to carry out
the skeletal isomerization before or after the esterification
reaction. Performing the isomerization reaction on the ester
was preferred over the fatty acid based on the trans
isomerization and cloud point results. Reducing the
unbranched trans isomers was desirable in obtaining a low
cloud point.
List of symbols
MO
OA
Methyl oleate
Oleic acid
CP
Cloud point
BC
Branch chain
FTIR
FFA
Fourier transform infrared spectroscopy
Free fatty acid(s)
FAME Fatty acid methyl ester(s)
GC/MS Gas chromatograph/mass spectrometry
Introduction
Branched chain fatty acids (FA) and fatty acid methyl
esters (FAME) have various applications. Branched FA
compounds have applications as detergents and surfactants
as well as uses in the lubricant industry. Branched FAME
could have uses as a biodiesel additive. Cold flow prop-
erties and oxidative stability are two important properties if
the branched chain FA and FAME are to be used as sur-
factants and fuel additives, respectively. FA are derived
from vegetable oils which are composed of both saturated
and unsaturated fatty acids. Saturated FA are stable,
whereas unsaturated FA with a C=C are unstable and
subject to oxidation [1]. Cold flow properties (cloud point
and viscosity) can be improved by the addition of a branch
chain [2]. Therefore, if the unsaturated fatty acid can be
branched then hydrogenated, it would have the stability of
a saturated FA or FAME, and should possess good cold
flow properties (low cloud point and viscosity). The
improvement of cold flow properties may allow the FAME
to be used as a biodiesel additive in order to improve the
cold flow properties and oxidative stability which are the
Keywords Fatty acid methyl ester Á Isomerization Á
Branch chain Á FTIR Á Cloud point
S. J. Reaume Á N. Ellis (&)
Chemical and Biological Engineering,
University of British Columbia,
2360 East Mall, Vancouver, BC V6T 1Z3, Canada
e-mail: nellis@chbe.ubc.ca
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J Am Oil Chem Soc (2011) 88:661–671
two major issues with biodiesel. If the addition of branched
chain FAME can give biodiesel a wider market use, a large
market is created for the reaction product since biodiesel
has many advantages over conventional diesel. Most
studies have shown a clear life-cycle reduction in CO2
emissions (e.g. 78% reduction reported by Tyson [3])
taking into account all fossil fuel energy used in crop
cultivation and production. There can also be economic
advantages to the use of biodiesel [4, 5].
the desired product, methyl isostearate, was formed with a
selectivity of 82%.
Branch chain isomerization can be performed on either
the fatty acid or a fatty acid methyl ester. The key pur-
pose for the isomerization is to improve the cold flow
properties of the compound and the stability through
hydrogenation. Therefore, the isomerization step could be
incorporated either before or after the esterification reac-
tion, according to Fig. 1. The purpose of testing the
isomerization reaction on both the FA and FAME is to
see which compound is better suited for the isomerization
reaction. Then either the necessary esterification/de-
esterification reaction can be performed to create the
desired FA or FAME.
FA and FAME can be branched using zeolite-based
solid acid catalysts which facilitate the skeletal isomeri-
zation of the hydrocarbon tail, to form a methyl or ethyl
side chain [6]. This reaction takes place in the pore space of
the zeolite material containing acid sites. The side chain
created from branching can lower the cloud point of the
fatty acid or fatty acid methyl ester. By lowering the cloud
point of a substance, the cold flow properties are improved
[7]. Alkyl branching of the hydrocarbon chain can be a
viable way of improving the cloud point. The mechanism
of the isomerization has been proposed by Martens and
Jacobs [8]. Inside the zeolite pore space the carbon–carbon
double bond forms a cyclic three or four carbon carbo-
cation ring within the hydrocarbon chain. This ring, being
unstable, loses a proton, opens up and the corresponding
methyl or ethyl side chain is formed. This process of car-
bocation formation and destruction can also cause a
migration of the double bond towards the carboxylic acid
group. As well at high temperatures, there is increased
cracking of the molecule, generating undesired products
[9].
Quantifying the conversion of the isomerization reaction
usually involves the use of gas chromatograph (GC) with a
mass spectrometer (MS). This method is often time con-
suming; and, the equipment necessary is often expensive to
acquire. Use of Fourier transform infrared spectroscopy
(FTIR) can be a simple, quick and low cost method of
quantifying conversion when GC/MS is not available.
FTIR measures the absorbance of the different bonds in a
compound or mixture of compounds. Using this feature,
compounds can be quantified by choosing a unique bond
specific to the compound [11–13]. A standard curve can be
generated using the absorbance of a particular bond as the
dependant variable and the concentration of the compound
as the independent variable. This method is particularly
useful for measuring the conversion of an isomerization
reaction due to the fact that isomerization changes the bond
structure of a compound. FTIR has been proven useful in
determining free fatty acid (FFA) content of oils [14–16].
There are limited studies in the literature on the use of
FTIR for quantifying conversion of reactions based on
changes in bond structure. Using the similar methods of
FFA quantification, determination of the change in bond
structure of fatty acids or fatty acid methyl esters (FAME)
can be accomplished.
Ideal conditions as stated by Koivusalmi and Jakkula
[10] for the isomerization of FA are temperatures of
220–300 °C, pressures of 0.1–2 MPa, and with water used
only as a co-catalyst of 1–3 wt%. The reaction is ideally
carried out in a batch process for approximately 5–6 h with
a zeolite catalyst loading of 1–10% [10]. Results from Yori
et al. [6], found two different optimal temperatures of 275
and 150 °C based on the reduction of the cloud point as
criteria. These authors found that the lower optimal tem-
perature of 150 °C was due to a reduced amount of coking
on the catalyst as compared to samples run at higher
temperatures. The optimal high temperature is due to the
increased fluidity and reaction rates that increase with
higher temperatures. The difference in the optimal tem-
peratures could be due to the unstable nature of the carbon–
carbon double bond. Ngo et al. [7], studied the effects of
different co-catalysts (water and methanol). The research-
ers performed the isomerization reaction on oleic acid
(C18:1) at 250 °C for 6 h and 2.5 wt% zeolite loading. A
maximum conversion of 99% oleic acid to products was
achieved in the presence of 2 wt% H2O based on the
amount of oleic acid used. Under the conditions utilized,
The objective of this study was to find the optimal
reaction conditions for the isomerization of methyl oleate
or oleic acid to their branched chain isomers, as well as to
investigate whether the isomerization step should occur
on the acid or the ester. With limited studies done on
optimizing reaction conditions for the zeolite catalyzed
branch chain formation, a full range of different temper-
atures, pressures, amounts of co-catalysts and starting
materials was examined. These conditions were evaluated
and optimized based on cloud point and conversion to
their respective branched chain isomers. Once these
conditions are optimized for the ideal compounds, future
studies can be applied to mixtures generated from vege-
table oils.
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J Am Oil Chem Soc (2011) 88:661–671
663
Pre-Esterification
R1COOCH2
R1COOH
Zeolite
RCOOH
+
RCOOCH3
H2SO4
R2COOH
R2COOCH
R3COOH
+
OH
O
R3COOCH2
+
CH3OH
3H2O
OH
+
Skeletal Isomerization O
HOOCH2
HOOCH
HOOCH2
3H2O
Esterification
Hydrolysis
Post-Esterification
R1COOCH2
KOH
Zeolite
R1COOCH3
R2COOCH
R3COOCH2
+
3CH3OH
R2COOCH3
R3COOCH3
OCH3
OCH3
O
+
O
Transesterification
Skeletal Isomerization
HOOCH2
HOOCH
HOOCH2
Fig. 1 Potential process for the combination of isomerization and esterification/de-esterification of fatty acids to branched chain fatty acids
Experimental Methods
based on literature studies [9, 17]; and after which point,
the reaction mixture was cooled to room temperature using
cooling water, and lastly the pressure was released before
the sample was removed from the autoclave. The sample
and catalyst were transferred to a 50-mL centrifuge tube.
The separation of catalyst from the sample was carried out
in an Allegra 25R Centrifuge at 12,000 rpm for 20 min at
room temperature. The ester samples were then transferred
to a 20-mL glass container and analyzed for cloud point,
FTIR absorbance and GC/MS analysis, while the fatty acid
samples were esterified according to the esterification
conditions. After analysis the samples were stored at 4 °C
and shaded from direct light.
Isomerization
The isomerization reactions were carried out in an Auto-
clave series mini-reactor purchased from Autoclave
Engineers (Div. of Snap-Title Inc.) (Erie, PA, USA) under
the various reaction conditions described in Table 1. The
mixture of methyl oleate (Acros Organics Fair Lawn, NJ,
USA), methanol (Acros Organics Fair Lawn, NJ, USA) (if
called for) and beta zeolite (Zeolyst International, Valley
Forge, PA, USA) of 2 wt% were charged into the autoclave
for the methyl oleate study. For the oleic acid (Fisher
Scientific, Fair Lawn, NJ, USA) experiments, water was
used in place of methanol as the co-catalyst. The beta
Esterification
˚
zeolite catalyst had a pore size of 5.5 9 5.5 A and
˚
7.6 9 6.4 A, a Si/Al molar ratio of 360 and surface area of
Methanol and fatty acid were used at a molar ratio of 10:1.
A catalyst of 2 wt% 95% sulfuric acid was mixed with the
methanol in a 100-mL glass reaction chamber until fully
dissolved. Next the fatty acid was added to the reaction
mixture and stirred at 300 rpm while heated under reflux
for 1.5 h. Once the reaction was complete the mixture was
washed with distilled water 3 times to separate the ester
from the methanol, acid and other impurities. Lastly, the
ester was dried with a desiccant pack (calcium chloride) to
remove any traces of water emulsified in the ester. The acid
value of the ester was taken according to ASTM D974-08
620 m2/g (Zeolyst International). The catalyst was pre-
calcined prior to experiments at 500 °C for 3 h and stored
at room temperature until it was used for the experiments.
The reaction mixture was mixed at a speed of approxi-
mately 600 rpm and purged with [99% N2 for 15 min to
remove all traces of oxygen prior to heating. The temper-
ature was ramped up to the desired temperature within
10 min while purging with N2. Once the temperature was
at the desired point the pressure was set to the desired
pressure (Table 1). The reaction was carried out for 5 h
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Table 1 FTIR results of methyl oleate and oleic acid isomerization
Experimental conditions
Experimental results
MO study
OA study
Conversion (%)
Conversion (%)
CP (°C)
CP (°C)
Run #
Temperature
(°C)
Pressure
(MPa)
H2O or methanol
(wt%)
BC-isomer
trans-Isomer
BC-isomer
trans-Isomer
C1
C2
1
23
250
200
225
250
275
300
200
225
250
275
300
200
225
250
275
300
0
0
0
0
2
1
0
2
1
0
2
2
0
2
1
0
1
1
0
0
0
0
-15.6
-15.7
-15.2
-12.9
-11.6
-8.1
0
0
0
0
-15.6
-15.6
-15.1
-13.4
-8.5
-6.7
-1.3
-8.1
-8.3
-0.1
2.9
1.5
0.1
0.1
0.1
0.1
0.1
1.5
1.5
1.5
1.5
1.5
3
14
0
1
34
20
14
36
42
25
31
20
12
50
33
31
40
27
5
12
39
52
51
54
57
57
57
57
54
35
39
42
65
64
2
3
3
21
11
12
33
19
25
31
22
36
25
40
17
22
8
4
28
40
0
5
16.2
6
-14.9
-14
7
3
8
8
-13.3
-12.2
-11.7
-15.2
-14.7
-14.9
-13.3
-11.8
9
16
30
0
10
11
12
13
14
15
0.3
-7.4
-4.9
-6.2
-0.7
0.7
3
0
3
5
3
13
23
3
C1 Control #1, C2 Control #2, BC Branch chain, MO Methyl oleate, OA Oleic acid, CP Cloud point
Table 2 Conversion to methyl oleate of isomerized oleic acid sam-
ples after esterification with 95% sulphuric acid in methanol
99.91% and acid values between 0.049 and 0.185 mg
KOH/g ester.
Run Acid value (mg KOH/g
#
Conversion to methyl oleatea
(%)
ester)
Instrumentation
1
0.156
0.128
0.096
0.185
0.146
0.163
0.056
0.142
0.187
0.151
0.123
0.151
0.049
0.135
0.131
99.93
99.94
99.95
99.91
99.93
99.92
99.97
99.93
99.91
99.93
99.94
99.93
99.97
99.93
99.94
The cloud point analysis was carried out on the Cloud, Pour
and Freeze Point Analyzer, Model PSA-70X, acquired from
Phase Technologies (Richmond, BC) with an accuracy of
1 °C. At the start of a run, a standard sample of known
cloud point was tested to be within 1 °C of the known cloud
point in order to ensure proper operation of the instrument.
The sample cup was then cleaned with heptane and then
flushed with 150 lL of sample twice. Next the sample of
unknown cloud point was tested, 150 lL of sample was
placed inside the analyzer and the temperature was lowered
at a rate of 1.5 °C/min until crystals first appeared. The
cloud point analyzer meets and complies with the ASTM
D5773 method for the testing of the cloud point.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
a
Infrared analysis was carried out on a Varian 3100 FTIR
equipped with an Attenuated Total Reflectance (ATR)
crystal. The absorbance of each sample was taken over the
wavelength range 4,500–650 cm-1. FTIR measures the
absorbance of each chemical bond or specific group i.e.,
–CH3 group of a compound. A 50-lL amount of each
sample was placed on a horizontal ZnSe crystal and
Remaining difference is oleic acid
method in order to ensure[99.9% conversion of fatty acid
to fatty acid methyl esters (FAME). Table 2 shows that the
esterification reaction achieved yields of no less than
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665
Optimization
samples were scanned 64 times and co-added together at a
resolution of 4 cm-1. The signal was analyzed using
Varian Resolutions Pro software which employed baseline
and ATR correct features.
The optimization was carried out with Minitab 15 software,
by means of a full factorial design. The factors used were
temperature, pressure and wt% co-catalyst. The responses
that were optimized were the conversion and cloud point of
the ester. The factorial design was a three-factor two-level
design according to the reaction conditions stated in
Table 1.
FTIR Quantification
The compound methyl 16-methyl heptadecanoate (Sigma–
Aldrich, Oakville, ON, Canada) was used as a branched
chain isomer for quantification. Standards were made in
methyl oleate at concentrations of 75, 50, 25, 10 and 0%.
Peaks of interest in the absorbance profile are 2,955 and
2,864 cm-1 which corresponds to the –CH3 and –CH2–
groups, respectively [11, 15]. The ratio of the 2,864/
2,955 cm-1 peaks were calculated and plotted against the
concentration of branched chain isomer and a standard
curve was generated with an R2 value of 0.99 in order to
calculate the concentration of branched chain fatty acid
methyl ester in the unknown samples. The ratio of peaks
was linear to the wt% of branch chain fatty acid methyl
ester in the sample analyzed. This allowed a linear equation
to be generated and fast accurate analysis of the conversion
to branch chain isomers.
Results and Discussion
FTIR Analysis
Methyl oleate was taken as a baseline sample for absor-
bances and all samples after undergoing isomerization
were compared for any change in absorbance peaks. The
peaks of interest altered after the isomerization reactions
were 2,955 cm-1 (–CH3 group), 2,864 cm-1 (–CH2–
group) and 968 cm-1 (trans –HC = CH– group) as shown
in Fig. 2. There was no other significant change to the
absorbance spectrum of the samples after each run.
The calibration of trans double bond formation was
similar to the branched chain fatty except that the com-
pound methyl elaidate (Sigma–Aldrich, Oakville, ON,
Canada) was used as the standard. The absorbance of the
trans double bond is at 968 cm-1 and a peak at 1,744
(C=O) was used to stabilize the reading by taking the ratio
of the two [11].
Methyl Oleate Study
As shown in Table 1, there is an increase in the cloud point
as the reaction temperature increases, with the pressure
having little effect on the cloud point, except for the 300 °C
and 0.1 MPa condition causing a sharp increase in the cloud
point. The cloud points of the different experimental con-
ditions range from -15.2 °C for 200 °C and 3.0 MPa (Run
11) to 16.2 °C for 300 °C and 0.1 MPa (Run 5) as shown in
Table 1. These results are consistent with the study by Yori
et al. [6], where the low temperature of 150 °C was the
The heights of the peaks were utilized for all absorben-
cies due to poor peak resolution, especially useful between
3,100 and 2,750 cm-1 where there was no full peak sepa-
ration. Taking the heights simplifies the analysis and
removes errors of area integration due to poor peak reso-
lution [11]. The second safeguard against error was taking
the ratio of two peaks, i.e., 2,864/2,955 cm-1 for branch
chain isomers and 968/1,744 cm-1 for trans isomers. This
removes the error due to variations from scan to scan.
GC/MS Method
GC/MS analysis and characterization was carried out on a
Varian CP 3800 gas chromatograph (Varian, Mississauga,
ON) equipped with a capillary WCOT fused silica
25 m 9 0.32 mm wax 52CP column with split ratio 10:1.
A Varian 4000-8 mass spectrometer set to scan from 30 to
350 m/z at a rate of 1.5 scans/s. Helium was the carrier gas
through the column at a rate of 2 mL/min. The injector
temperature was set at 280 °C and the column was initially
set at 150 °C for 0.5 min; ramped at 5 °C/min to 200 °C
and held for 2 min; then ramped to 250 °C at 5 °C/min and
held for 5 min, for a total time of 27 min.
Fig. 2 FT-IR absorption spectra of isomerized methyl oleate under
the reaction conditions of 250 °C and 0.1 MPa
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J Am Oil Chem Soc (2011) 88:661–671
optimal reaction temperature for decreasing the cloud point
of biodiesel, using a similar zeolite-based catalyst and a
temperature range of 125–275 °C in nitrogen gas at atmo-
spheric pressure. The conversion of methyl oleate to bran-
ched chain esters under the various reaction conditions has
also been investigated. However, the conversion to bran-
ched chain isomers does not follow any specific temperature
dependence, indicating reaction temperature is not a sig-
nificant factor within the range studied. Increasing the
pressure of the reaction increased the conversion, but only
at low temperatures (200–250 °C). Branch chain conver-
sion ranges from 0 to 40% for reaction conditions 225 °C
and 0.1 MPa and 250 °C and 3.0 MPa (Runs 2 and 13 in
Table 1), respectively.
advantages that branching the hydrocarbon chain can have
on the cloud point of the biodiesel.
Oleic Acid Study
Isomerization reactions were carried out on oleic acid
under the reaction conditions of 200–300 °C and
0.1–3 MPa with 0–2 wt% co-catalyst. After the isomeri-
zation reaction was completed, the mixture was centrifuged
and esterified to create an ester as previously stated. The
OA (oleic acid) cloud point results, shown in Table 1,
increased with increasing reaction temperature: ranging
from -15.1 °C for Run 1 (200 °C and 0.1 MPa) to 2.9 °C
for Run 9 (275 °C and 1.5 MPa). The increase in pressure
from 0.1 to 1.5 MPa increased the cloud point in every
case; whereas, an increase from 1.5 to 3.0 MPa did not
consistently raise the cloud point. The rise in cloud point
can be explained again by the unwanted side reaction of
cis double bond configuration conversion to trans
configuration.
Experimental reproducibility was tested by running
triplicates of two experimental conditions chosen at ran-
dom. The standard deviation of the results were calculated
as 3.2 and 2.1% for Runs 1 (200 °C and 0.1 MPa), and 3
(250 °C and 0.1 MPa), respectively. Therefore, the dif-
ference in results had to be [4% for the difference to be
significant. The cloud point analysis was also repeated
and the deviation is within the 1 °C accuracy of the
instrument which confirmed the reproducibility of the
results.
The OA branch chain conversion results (Table 1) are
very erratic, with no clear pattern that emerges. The values
range from 4% for Run 15 (300 °C and 3.0 MPa) to 51%
conversion for Run 10 (300 °C and 1.5 MPa), which cor-
respond to a study by Zhang and Zhang [17] showing a
branch chain conversion range of approximately 8–40%
using a variety of different catalysts. Most of the results
from this work show conversion to branch chain products
to be in the 30–40% range. This is consistent with the
results of Ha et al. [19], and Tolvanen et al. [20], who have
reported conversions of 32 and 30% branch chain isomers,
respectively, using a zeolite based catalyst and oleic acid
and linoleic acid as a starting material.
The rise in cloud point with increasing reaction tem-
perature is due to the undesired isomerization reaction
which changes the cis double bond configuration to a trans
double bond within the molecule. The change in bond
configuration is also what explains the rise in cloud point.
The melting point of a substance is an indicator of its cloud
point, therefore, for example, methyl elaidate (trans double
bond ester) has a much higher melting point of 9 °C [2]
than that of cis double bond ester methyl oleate -20 °C
[18]. This trans/cis isomerization ratio increases as reaction
temperature increases, and decreases with increasing
reaction pressure. The MO (methyl oleate) runs in Table 1
show a substantial increase in cloud point from -8.1 °C
(275 °C and 0.1 MPa) to 16.2 °C (300 °C and 0.1 MPa)
which was due to the sharp increase in trans bond forma-
tion of 28–41%, respectively, and negligible increase in
branch chain formation. A comparison of the cloud point
results versus the branch chain and trans isomer isomeri-
zation results shows that trans isomers have a much greater
negative effect on the cloud point than the potential posi-
tive effect of branching the hydrocarbon. A case where the
branch chain formation directly affects the cloud point is
shown in Table 1 for the MO runs between Run 1 (200 °C
and 0.1 MPa) and Run 2 (225 °C and 0.1 MPa). The cloud
point increases from -15.2 to -12.9 °C, and the branch
chain conversion decreases from 14 to 0%, respectively;
while, there is negligible increase in the trans bond isom-
erization. The presence of the trans bond esters causes a
rise in the cloud point of the mixture. This illustrates the
An emerging pattern is the correlation between the trans
isomer conversion, branch chain conversion and cloud
point. There are two cases where cloud point decreases
with increasing temperature for the OA study. First case,
by increasing the temperature from 275 to 300 °C at
1.5 MPa, the cloud point of 2.9 °C decreases to 0.3 °C,
while the branch chain conversion increases from 12 to
50% with negligible change in trans isomer conversion.
Therefore the drastic increase in branch chain isomer could
have had a positive effect on the cloud point. A second case
is the decrease in cloud point from -4.9 °C (225 °C and
3.0 MPa) to -6.2 °C (250 °C and 3.0 MPa), while the
trans isomer conversion is negligible and the branch chain
conversion increases from 32 to 41% in the OA study, as
shown in Table 1. The second case takes less of an increase
in branch chain isomers to affect cloud point because the
trans isomer conversion is lower: 57% compared to 40% in
cases one and two, respectively. These two results indicate
that branching has the potential to decrease the cloud point
by at least 2.5 °C given the proper conditions.
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GC/MS Analysis
667
The slight discrepancy between the GC/MS and FTIR
results can be attributed to two factors. First the FTIR
detects the trans configuration of the carbon–carbon double
bond in both the branched and unbranched compounds,
whereas the GC/MS separates the compounds and mea-
sures them individually (i.e. (3) and (2.1–2.4) in Tables 3
and 4); therefore, giving two different results. A second
reason is the effect of the CH3 group on the IR absorbance
of the C=C bond. The peak used to quantify the trans
double bond is the group R1HC=CHR2. The group fre-
quency for the unbranched molecule (R1HC=CHR2) is in
the range of 980–960 cm-1. When a methyl branch is
added, this changes the group to R1R3C=CHR2, thus
affecting the intensity and widening the peak [22]. How-
ever, overall results from the GC/MS analysis support the
FTIR findings of bond rearrangement with respect to the
reaction conditions.
A GC/MS analysis was performed on the products of the
reaction conditions 1–15 for both starting material in order
to identify the compounds and verify the FTIR results. The
MS analysis of the results showed various compounds,
some detected by the FTIR analysis and others that were
not. Figure 3 shows a typical GC spectra obtained at
reaction conditions 250 °C and 0.1 MPa. GC/MS analysis
results are summarized in Tables 3 and 4 for the methyl
oleate and oleic acid starting material, respectively. The
MS analysis has identified four different trans methyl oc-
tadecenoates. These products are formed from carbocation
formation, migration and reforming as a trans double bond
at the various carbons without branching [21]. The con-
centration of the various trans bond esters decreases as the
double bond position is shifted farther from the original 9
position, with the concentration of position 9 [ position
11 [ position 8 [ position 6. The trend is held constant,
with the overall amount increasing with temperature. The
increase in temperature increases the degree of double
bond migration with the high temperatures having the
greatest amount of methyl 6-octadecenoate due to the
higher reaction rates at higher temperatures.
Three products identified by the GC/MS analysis and
not through FTIR analysis were methyl hydroxyoctadece-
noates, stearolactones and cracked products. These prod-
ucts were not picked up by the FTIR because they do not
differ significantly in bond structure and exist at small
concentrations of \3% for the hydroxyl esters and the
stearolactones and \5% for the cracked products. These
compounds also only exist in samples run at high tem-
peratures, i.e.,[250 °C. Their effect on cloud point would
be minimal, since C14–C16 and hydroxyl esters have a
lower melting point and therefore, a lower cloud point than
that of the methyl octadecenoates [2, 18]. Therefore, using
melting points as indicators of cloud points, these three
species would not have a significant effect on increasing
cloud point of the samples.
The overall conversion of methyl oleate increases with
increasing temperature and is the highest with the median
pressure value of 1.5 MPa. As conversion increases so does
the cloud point of the sample in all but one of the cases.
The oleic acid starting material reaction at 275 °C and
1.5 MPa has a conversion of 75% with a cloud point of
2.9 °C; while, under 300 °C and 1.5 MPa reaction condi-
tions, has a cloud point of 0.3 °C with a conversion of 80%.
This decrease in cloud point is most likely due to the sig-
nificant rise in methyl isooctadecenoates from 25 to 50%,
respectively. The methyl isooctadecanoates are grouped
together in the results due to the inability of the MS to
differentiate between the limited branched fatty acids in the
library.
Optimization Study
An optimization study was conducted to examine the
effects of the co-catalyst on the cloud point and branch
chain conversion of the various reaction products. There is
evidence in the literature that supports the idea of using
water or methanol to improve the conversion of the
isomerization reaction by facilitating the transfer of the
protons [7, 10, 20]. Beta zeolite being an acid catalyst, it
will catalyze the esterification/de-esterification reactions.
Therefore, this study uses water for the oleic acid experi-
ments and methanol for the methyl oleate experiments in
order to prevent these reactions from taking place. The use
of a factorial design allows for the user to get the maximum
amount of data from a reasonable amount of experiments
[23]. A secondary purpose to the optimizations study is to
find an optimal set of reaction conditions. The conditions
studied were temperature, pressure and wt% co-catalyst.
The responses that were optimized were the branch chain
conversion (BC) and cloud point (CP) of methyl oleate
Fig. 3 GC analysis of reaction products of isomerized ester at
reaction condition 250 °C and 0.1 MPa, 1 cis-methyl octadecenoate,
2 trans-methyl octadecenoate, 3 methyl isooctadecenoates, 4 methyl
hydroxyoctadecenoate 5 c-stearolactone and 6 Shorter chain methyl
hexa-, penta- and tetradecenoates (cracked products)
123

668
J Am Oil Chem Soc (2011) 88:661–671
Table 3 GC/MS analyzed isomerization products of methyl oleate
Run #
Temperature
(°C)
Pressure
(MPa)
Water
(wt%)
Conversiona
(%)
Area (wt%)b
Cloud point (°C)
3
2.1
2.2
2.3
2.4
5
6
4
C1
C2
1
23
250
200
225
250
275
300
200
225
250
275
300
200
225
250
275
300
0
0
0
0
2
1
0
2
1
0
2
2
0
2
1
0
1
1
0
3
0
0
0
0
0
0
0
0
1
2
3
0
0
1
3
3
0
0
2
1
2
0
0
0
0
0
2
3
0
0
0
0
2
0
0
0
0
1
0
0
0
0
0
1
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
2
0
0
1
2
2
0
1
1
2
1
0
2
0
0
1
1
3
0
0
0
2
3
0
1
1
1
2
0
0
0
0
0
1
2
0
0
0
0
1
0
0
1
0
1
-15.6
-15.7
-14.6
-12.9
-11.6
-8.1
1.5
0.1
0.1
0.1
0.1
0.1
1.5
1.5
1.5
1.5
1.5
3.0
3.0
3.0
3.0
3.0
24
15
30
35
37
28
23
35
42
47
19
15
24
29
33
15
8
2
2
3
3
19
11
10
23
9
4
4
8
5
10
1
16.2
6
-14.9
-14
7
2
8
25
23
22
16
10
18
17
22
3
-13.3
-12.2
-11.7
-15.2
-14.7
-14.9
-13.3
-11.8
9
4
10
11
12
13
14
15
5
1
1
3
4
4
3 Methyl Isooctadecenoates, 2.1 trans-methyl 9-octadecenoate, 2.2 trans-methyl 11-octadecenoate, 2.3 trans-methyl 8-octadecenoate, 2.4 trans-
methyl 6-octadecenoate, 5 stearolactone, 6 Shorter chain methyl esters (cracked products), 4 methyl hydroxyoctadecenoate, C1 control #1 no
reaction pure product, C2 control #2 exposed to median reaction conditions for 5 h with no catalyst
a
Conversion is defined as (100 - unreacted methyl oleate) 9 100%
b
GC separated area curves using dodecane as internal standard
(MO) and esterified oleic acid (OA), as summarized in
Table 5. The optimal predicted conditions were experi-
mentally verified to check the accuracy of the model as
shown in Table 5. The results are organized to show the
optimal conditions of each of the responses separately, and
in various combinations. The optimal response for the
combination of all four factors is 200 °C, 1.25 MPa and
0 wt% co-catalyst.
literature is used where cloud point data is lacking. The
melting point of methyl stearate is 38 °C and the branched
chain isomer methyl 16-methylheptadecanoate is 27 °C
[2]; therefore, branching the chain provides advantages in
lowering the melting point of a substance and subsequently
the cloud point. The undesired side reaction of cis to trans
double bond isomerization eliminates any reduction caused
by the branching of the molecule. Methyl oleate (cis con-
figuration) has a melting point of -20 °C and methyl
elaidate (trans configuration) has a melting point of 9 °C
[2]. Thus the potential 11 °C reduction from branching is
negated by the possible 29 °C increase from the cis to trans
double bond isomerization.
The two highest predicted values for branch chain
conversion and cloud point were 53% and -17.5 °C,
respectively. The highest branch chain conversion was for
when oleic acid was isomerized; while, the lowest cloud
point was when methyl oleate was isomerized. Therefore
two contour plots of isomerized methyl oleate and oleic
acid branch chain conversion, Figs. 4 and 5, respectively,
were created to show the combined effect of the reaction
conditions. From these plots it is clear that the optimal
conditions do reflect the conditions predicted by the opti-
mization study.
The results of the study all showed an increase in cloud
point from the control values (-15.6 and -15.7 °C), which
was not the intended goal of the study. However, an
examination of the reaction products and research into the
isomerization mechanism provides an understanding as to
why the cloud points have increased. The mechanism for
the branching of unsaturated fatty acids, forms a carbo-
cation ring structure at the double bond, followed by the
carbocation ring breaking and reforming the double bond
and a methyl or ethyl side chain [8, 9, 24]. This process of
double bond reforming changes the configuration of the
Melting Point and Mechanism
Melting points of a substance are accurate indicators of
cloud points; therefore, melting point data from the
123

J Am Oil Chem Soc (2011) 88:661–671
669
Table 4 GC/MS analyzed isomerization products of esterified oleic acid
Run
#
Temperature
(°C)
Pressure
(MPa)
Water
(wt%)
Conversiona
(%)
Area (wt%)b
Cloud point
(°C)
3
2.1
2.2
2.3
2.4
5
6
4
C1
C2
1
23
250
200
225
250
275
300
200
225
250
275
300
200
225
250
275
300
0
0
0
0
2
1
0
2
1
0
2
2
0
2
1
0
1
1
0
3
0
0
0
0
0
0
1
4
3
4
5
1
3
5
6
5
1
4
6
6
8
0
0
2
3
3
3
3
1
2
2
5
4
1
2
3
3
6
0
0
1
2
2
2
2
0
1
3
3
3
1
2
1
3
5
0
0
0
0
1
0
0
1
3
3
3
0
1
1
3
2
2
0
2
2
3
3
2
3
2
4
3
4
4
3
3
2
2
2
0
0
0
0
1
1
2
0
0
2
2
2
0
1
1
2
2
-15.6
-15.7
-15.1
-13.4
-8.5
-6.7
-1.3
-8.1
-8.3
-0.1
2.9
1.5
0.1
0.1
0.1
0.1
0.1
1.5
1.5
1.5
1.5
1.5
3.0
3.0
3.0
3.0
3.0
31
42
63
57
69
42
50
67
75
80
42
63
65
70
71
22
19
24
34
42
28
29
22
25
50
27
25
41
21
10
2
2
5
3
8
4
7
5
9
6
5
7
5
8
10
15
8
9
10
11
12
13
14
15
0.3
3
-7.4
-4.9
-6.2
-0.7
0.7
9
8
10
16
3 Methyl Isooctadecenoates, 2.1 trans methyl 9-octadecenoate, 2.2 trans-methyl 11-octadecenoate, 2.3 trans-methyl 8-octadecenoate, 2.4 trans-
methyl 6-octadecenoate, 5 stearolactone, 6 Shorter chain methyl esters (cracked products), 4 methyl hydroxyoctadecenoate, C1 control #1 no
reaction pure product, C2 control #2 exposed to median reaction conditions for 5 h with no catalyst
a
Conversion is defined as (100 - unreacted methyl oleate) 9 100%
b
GC separated area curves using dodecane as internal standard
Table 5 Response optimization of reaction conditions based on cloud point (°C) and branch chain conversion (wt%)
#
Factors
optimized
Optimal reaction conditions
Response
(predicted)
Response
(experimental)
Differencea
(%)
Temperature
(°C)
Pressure
(MPa)
co-catalyst (wt%)
1
2
3
4
5
CP (MO)
CP (OA)
200
200
200
300
200
0.1
0.1
3
2
0
0
0
0
-17.5
-15.2
39
-15.8
-15.5
36
9.7
-2.0
7.6
BC (MO)
BC (OA)
CP (MO) &
BC (MO)
CP (OA) &
BC (OA)
CP (MO),
CP (OA),
BC (MO) &
BC (OA)
1.5
3
53
50
5.7
-16.7
39
-15.4
35
7.8
10.3
-2.0
-11.1
2.0
6
7
200
200
0.1
0
0
-15.2
36
-15.5
40
1.25
-15.2
-11.6
25
-14.9
-12.2
31
-5.2
-24.0
-25.0
32%
40%
CP cloud point, BC branch chain product, MO methyl oleate starting material, OA oleic acid starting material esterified post reaction
a
% difference of predicted versus experimental results
double bond from the cis configuration to the trans con-
figuration. This is due to the fact that it is thermodynami-
cally more stable to reform as a trans bond [25, 26]. The
experimental results show that there is trans isomers
formed without concomitant branching. Therefore, when
the double bond is reformed it may or may not reform with
123

670
J Am Oil Chem Soc (2011) 88:661–671
at 300 °C and 1.5 MPa). This contrast between optimal
branching and optimal cloud point is due to the fact that
increasing the temperature had the negative effect of
increasing the cloud point of the samples. The rise in cloud
point was due to the undesired side reaction of trans
isomerization, which straightens the hydrocarbon chain
thereby increasing the cloud point. Although GC/MS
analysis detected small concentrations of hydroxyl side
chains and cracked products, they did not possess the high
melting point of the trans bond methyl esters or large
enough concentrations to significantly affect the cloud
point. Though there is a potential benefit to creating a
branch chain isomer, efforts are needed to reduce the
amount of unbranched trans isomer production. The ideal
goals of this study were to branch the FA and FAME as
well as lower the cloud point. Although the first objective
was accomplished, the cloud point of the FAME was not
improved. However, this study provided an insight as to
why creating a branch chain can negatively affect the cold
flow properties of the methyl oleate.
Fig. 4 Contour plot of two-way interaction of temperature (°C) and
pressure (MPa) on cloud point (°C) for isomerization reactions carried
out on methyl oleate
Acknowledgments The authors wish to acknowledge the financial
contribution of the Natural Sciences and Engineering Research
Council of Canada.
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