Application of metal triflate catalysts for the trans-esterification of Jatropha curcas L. oil with methanol and higher alcohols

Article abstract of DOI:10.1007/s11746-013-2364-3

This paper describes an experimental study on the application of metal triflate salts for the (trans-) esterification of fatty esters (triolein, methyl oleate, methyl linoleate), fatty acid (oleic acid), as well as Jatropha curcas L. oil with methanol and higher alcohols (ethanol, n-propanol, iso-propanol, iso-butanol, tert-butanol). The effect of the metal type (scandium, bismuth, aluminium, lanthanum, copper, zinc) and process conditions on reaction performance were evaluated. Highest conversions were obtained with Al(OTf) ₃. Reaction of triolein with methanol gave 99 mol% conversion at 165 C for 1 h and the main product was the methyl ester. In addition, partial methoxylation of the carbon-carbon double bonds in the fatty acid chains was observed, though their fraction in the mixture was less than 20 mol%. The trans-esterification reaction was also successfully performed using higher alcohols, giving >95 % conversions for ethanol, n-propanol, iso-propanol and iso-butanol, whereas tert-butanol was not reactive. For the reaction of oleic acid with methanol, quantitative esterification, partial methoxylation of the carbon-carbon double bonds and the formation of small amounts of a lactone was observed. The methodology using Al(OTf)₃ was successfully performed on the trans-esterification reaction of JO (FFA content of 2.1 wt%) with various alcohols. Key properties (viscosity, pour point and cloud points) of the (branched) Jatropha esters were determined. The best cold-flow properties were obtained for the iso-propyl esters of JO, with cloud point and pour point of -3 and -24 C, respectively.

Full text of DOI:10.1007/s11746-013-2364-3

J Am Oil Chem Soc (2014) 91:325–336
DOI 10.1007/s11746-013-2364-3
ORIGINAL PAPER
Application of metal triflate catalysts for the trans-esterification
of Jatropha curcas L. oil with methanol and higher alcohols
•
Louis Daniel Carolus B. Rasrendra
•
•
Arjan Kloekhorst Antonius A. Broekhuis
•
•
Robert Manurung Hero J. Heeres
Received: 27 April 2013 / Revised: 20 September 2013 / Accepted: 23 September 2013 / Published online: 24 October 2013
Ó AOCS 2013
Abstract This paper describes an experimental study on
the application of metal triflate salts for the (trans-) ester-
ification of fatty esters (triolein, methyl oleate, methyl
linoleate), fatty acid (oleic acid), as well as Jatropha cur-
cas L. oil with methanol and higher alcohols (ethanol,
n-propanol, iso-propanol, iso-butanol, tert-butanol). The
effect of the metal type (scandium, bismuth, aluminium,
lanthanum, copper, zinc) and process conditions on reac-
tion performance were evaluated. Highest conversions
were obtained with Al(OTf)3. Reaction of triolein with
methanol gave 99 mol% conversion at 165 °C for 1 h and
the main product was the methyl ester. In addition, partial
methoxylation of the carbon–carbon double bonds in the
fatty acid chains was observed, though their fraction in the
mixture was less than 20 mol%. The trans-esterification
reaction was also successfully performed using higher
alcohols, giving [95 % conversions for ethanol, n-propa-
nol, iso-propanol and iso-butanol, whereas tert-butanol was
not reactive. For the reaction of oleic acid with methanol,
quantitative esterification, partial methoxylation of the
carbon–carbon double bonds and the formation of small
amounts of a lactone was observed. The methodology
using Al(OTf)3 was successfully performed on the trans-
esterification reaction of JO (FFA content of 2.1 wt%) with
various alcohols. Key properties (viscosity, pour point and
cloud points) of the (branched) Jatropha esters were
determined. The best cold-flow properties were obtained
for the iso-propyl esters of JO, with cloud point and pour
point of -3 and -24 °C, respectively.
Keywords (Trans-) esterification ꢀ Alkoxylation ꢀ
Isomerisation-c-lactonisation ꢀ Biodiesel ꢀ Metal
triflates ꢀ Cold-flow properties
Introduction
Biodiesel (fatty acid methyl esters) is an important biofuel
with an estimated global production volume of nearly 1.1
billion gallons in 2011 [1]. Favorable product properties
like high flash point, relatively low viscosity, and only a
marginal lower energy content than conventional diesel
makes biodiesel a good substitute for fossil diesel in the
industry and transportation sectors [2].
A point of concern is the cold-flow properties, expressed
in terms of pour point and cloud point, particularly in
countries with winter temperatures below 0 °C, leading to
plugging and poor combustion performance [2–4]. The
pour point of biodiesel is known to be a function of the
degree of unsaturation of the fatty acid chains and the
average fatty acid chain length and as such is a function of
the plant oil source, see Fig. 1 for details. A combination of
a high degree of unsaturation and a higher average chain
length leads to a lowering of the pour point and, thus, has a
positive effect on the cold-flow properties. This relation
only holds for oils with average FA chain lengths between
17 and 19, for oils with a much smaller average chain
length, for example coconut oil; this relation is not valid.
L. Daniel ꢀ C. B. Rasrendra ꢀ A. Kloekhorst ꢀ
A. A. Broekhuis ꢀ H. J. Heeres (&)
Department of Chemical Engineering, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, The Netherlands
e-mail: h.j.heeres@rug.nl
C. B. Rasrendra
Department of Chemical Engineering, Bandung Institute
of Technology, Bandung, Indonesia
R. Manurung
Department of Bioengineering, Bandung Institute
of Technology, Bandung, Indonesia
123

326
J Am Oil Chem Soc (2014) 91:325–336
Fig. 1 Effect of a degree of unsaturation, and b the average chain length of fatty acid methyl esters on pour point (adapted from [5])
Table 1 Cold-flow properties (CP and PP) of fatty acid alkyl esters
Oil source
Ester group
Methyl
References
Ethyl
n-propyl
Iso-propyl
n-butyl
Iso-butyl
2-butyl
Soybean
Canola
1.4/1.0
-1.4/-5.0
-8.2/-10.7
-2.9/-5.3
-7.6/-12.0
-7.9/-12.0
[7]
[8]
[8]
[8]
[8]
[8]
1.0/9.0
1.0/6.0
8.0/6.0
6.0/6.0
1.0/5.0
15.0/12.0
7.0/12.0
6.0/16.0
Palm
13.0/16.0
n.a./6.0
2.0/3.0
Safflower
Sunflower
Beef tallow
17.0/15.0
12.0/9.0
8.0/0.0
9.0/6.0
8.0/3.0
First value is the CP (°C), second value is the pour point (°C)
In addition to a proper choice of the pure plant oil
source, the use of cold-flow improvers or other alcohols
than methanol in the trans-esterification reaction have been
proposed [6]. An overview on the effect of the application
of higher alcohols instead of methanol on cold-flow prop-
erties for various plant oil sources is given in Table 1. The
use of higher alcohols and particularly branched alcohols
instead of methanol in general leads to an improvement in
the cold-flow properties.
esterification reaction is much faster at similar conditions
and, with 1 mol% of catalyst, essentially quantitative
yields were obtained for Sc(OTf)3 in 1 min. Scandium and
indium triflate (1–10 mol%) have also been shown to be
active catalysts for the trans-esterification of lipids in algal
biomass with ethanol in
a temperature range of
200–235 °C (1–20 molar excess) [12].
We here describe a study on the use of metal triflate
catalysts for the synthesis of fatty esters using higher
alcohols (C2–C4 alcohols). To the best of our knowledge,
the use of C3–C4 alcohols is an absolute novelty of this
paper as such catalysts have been explored for methanol
and ethanol only. A catalyst screening study on two model
reactions, viz., the trans-esterification of triolein and the
esterification of oleic acid using a range of metal triflates
and conventional heating is reported. The effects of the
length and type of the alcohol (primary, secondary, ter-
tiary) on catalyst performance were studied. Finally, the
best catalysts were also tested for a typical example of a
plant oil [Jatropha curcas L. oil (JO)] using microwave
heating. Relevant product properties (viscosity, pour and
Conventional biodiesel synthesis using acid or base
catalysis with higher alcohols is often more cumbersome
than for methanol [8, 10]. Full conversion of the oil is more
difficult to achieve due to lower reaction rates [9].
Recently, metal triflate catalysts have been introduced for
fatty ester synthesis. Scandium and bismuth triflate were
shown to catalyse the (trans-) esterification of free fatty
acids (FFA) and triglycerides very efficiently [11]. For
example, the trans-esterification of triolein using scandium
or bismuth triflate (10 mol%) and MeOH (48 molar excess)
at 150 °C for 20–25 min gave a methyl oleate in 92 %
(Sc(OTf)3) and 85 % ((Bi(OTf)3) yield. For oleic acid, the
123

J Am Oil Chem Soc (2014) 91:325–336
327
cloud point) of the product esters were determined and
structure-property relations were derived.
spectra library. Helium was used as the carrier gas at a flow
rate of 0.6 ml/min. The oven temperature was kept at
120 °C for 5 min and heated up to 250 °C at a rate of 3 °C/
min, and then held at 250 °C for 15 min. The injector
temperature was set at 250 °C.
Experimental Section
The cloud and pour point were determined using a Mini
Pour/Cloud Point tester model MPC-102A/102L from Ta-
naka Scientific Limited (Tokyo, Japan), using the L mode
with detection intervals of 1 °C. The measurements were
performed in triplicate and the average value is given.
The acid value of the starting material and products
were determined using a slightly modified procedure
reported by the National Cottonseed Products Association
(Method number 28.029). The product (0.1 g) was
weighed, dissolved in a mixture of diethyl ether and eth-
anol (50/50 %-v/v) (20 mL), and then titrated with a
0.01 N KOH solution.
Materials
Unrefined JO was obtained from Diligent Energy BV
(Eindhoven, The Netherlands). The oil was stored at 6 °C
for at least 10 h and the residue was filtered [13]. Refined
JO was prepared by degumming, deacidification, bleach-
ing, and deodorisation using a method described in [14].
Metal triflate catalysts ([99.0 %), alcohols ([98.0 %,
dried using MgSO4 and stored on molecular sieves before
use), sodium methoxide (25 % in methanol), triolein
([97.0 %), tristearine ([99.0 %), oleic acid ([99.0 %),
methyl oleate (99.0 %), triacetine, [99.0 %), methyl tert-
butyl ether (98.0 %), and chloroform-d (99.8 atom %D)
were obtained from Sigma-Aldrich (Steinheim, Germany).
MgSO4 (dry) was from Boom BV (Meppel, The Nether-
lands). All materials were used as received unless other-
wise stated.
The viscosity of JO and modification products was tes-
ted using a cone-and-plate rheometer AR1000-N from TA
Instrument with a cone of 40 mm in diameter with a 2°
angle. The viscosity measurements were conducted at
40 °C for 900 s, with a shear rate of 10 s-1
.
Elemental analyses (C and H content) were carried out
using an automated Euro EA3000 CHNS analyser with
acetanilide as a calibration reference. All samples were
analysed at least in duplicate and the average value is
given. The theoretical values are based on the chemical
composition of the products (GC analyses) and, when rel-
evant, include the fraction of alkoxy groups in the products.
Methods
Batch experiments with JO and metal triflates as the cata-
lysts were performed in a microwave reactor (Discover and
Explorer SP Microwave Synthesizers from CEM’s Focu-
sedTM Microwave Technology purchased from Beun de
Ronde (Abcoude, The Netherlands). Screening reactions
were performed in glass ampoules (outside diameter 8 mm,
inside diameter 5 mm, length 15 cm) using conventional
heating in an oven. This experimental approach was
applied to minimise reagent, solvent and catalyst use. The
ampoules were filled with the reagents and solvent and
sealed with a torch. Maximum pressure in both reactor
configurations is about 21 bars and this limits the upper
temperature of a reaction. Using vapour pressure curves
based on the Antoine equation [15], 165 °C was selected as
the maximum reaction temperature for methanol and
180 °C for all higher alcohols. Initial studies (not shown
here) showed that the results using conventional heating in
glass ampoules and a microwave set-up are comparable.
1H NMR analyses of JO and derivatives were performed
on an Oxford AS400 NMR Spectrometer whereas 13C
NMR analyses were performed on an Oxford AS200 NMR
Spectrometer. CDCl3 was used as the solvent.
Analytical Data for the JO Used in this Study
Crude JO
1H NMR (400 MHz, CDCl3) d 5.36 (m, –CH = CH–),
5.26 (m, OCH(CH2)2), 4.29 (dd, J = 11.8, 4.2 Hz,
OCH(CH2)2), 4.14 (dd, J = 11.9, 5.9 Hz, OCH(CH2)2),
2.76 (t, J = 6.1 Hz, = CH–CH2–CH =), 2.30 (t,
J = 7.4 Hz, –CH2COO–), 2.11–0.99 (m, –CH2–), 0.87 (t,
J = 5.0 Hz, –CH3, end group). 13C NMR (50 MHz,
CDCl3) d 173.0 (–COO–), 127.9–130.1 (CH=CH), 69.1
(–OCH(CH2)2), 62.2 (–(CH2)2CHO–), 22.8–34.4 (–CH2–),
14.3–14.4 (–CH3, end group).
Elemental analysis, calculated: C 76.7 %, H 11.9 %.
Found: C 77.3 %, H 11.3 %.
Acid value: 4.2 mg KOH/g oil.
Catalytic Reactions
GC–MS spectra for structural analysis of the products
were recorded on a HP 5890 equipped with a sol–gel
capillary column (length 30 m, inside diameter 0.25 mm,
and film thickness 0.25 lm) and a mass selective detector.
Peak identification was done using the NIST05a mass
Trans-Esterification of JO with Methanol
The trans-esterification reaction of JO with methanol was
performed using refined JO. The reaction was performed as
123

328
J Am Oil Chem Soc (2014) 91:325–336
1
follows: JO (10 g, 11.5 mmol of triglyceride), 25 wt%
sodium methoxide in methanol (0.34 mL, 1.5 mmol of
sodium methoxide), and methanol (2.8 mL, 69 mmol) were
placed in a three-necked round bottom flask. The mixture
was allowed to react under vigorous stirring at 65 °C for
3 h. The resulting emulsion/dispersion was cooled to room
temperature. The solids were removed by dropwise addition
of water at room temperature without stirring. The liquid
was collected and subjected to a centrifugation step to
obtain a clear transparent phase. The water addition/cen-
trifugation step was performed three times. The remaining
methanol and water were separated from the esters at ele-
vated temperatures under reduced pressure (T = 50 °C,
in the mixture, gmethoxy, are based on integration of H
NMR spectra using the following equations:
gmethyl½mol%ꢁ
Peak area of CH3 methyl esters ð3:69 ꢂ 3:52ppmÞ
¼
Peak area of CH3 end groups ð0:92 ꢂ 0:72ppm)
ꢃ 100%;
gmethoxy½mol%ꢁ
Peak area of CH3 methoxy group ð3:31 ꢂ 3:22ppmÞ
¼
Peak area of CH3 end groups ð0:92 ꢂ 0:72ppm)
ꢃ 100%:
1
30 mbar) for 4 h. The methyl ester, 1, was analysed by H
and 13C NMR and elemental analyses.
The fraction of other alkyl esters, galkyl, and alkyl esters
with alkoxy groups, galkoxy, was calculated using a similar
method as defined above.
Methyl Esters of JO, 1 1H NMR (400 MHz, CDCl3) d
5.35 (m, –CH = CH–), 3.63 (s, COOCH3, methyl ester),
2.78 (t, J = 6.2 Hz, = CH–CH2–CH =), 2.27 (t,
J = 7.5 Hz, –CH2COO–), 2.12–1.05 (m, –CH2–), 0.83 (t,
J = 7.0 Hz, –CH3). 13C NMR (50 MHz, CDCl3) d 174.2
(–COO–), 130.0–127.9 (CH=CH), 51.5 (COOCH3, methyl
ester), 34.0–22.5 (m, –CH2–), 14.0 (–CH3, end group).
Isolated yield: 9.97 g (95 wt% of theoretical yield).
Elemental analysis, calculated: C 77.0 %, H 12.1 %.
Found: C 76.9 %, H 12.1 %.
Preparative Trans-Esterification Reactions of JO
with Higher Alcohols
The preparative trans-esterification reactions of JO with
higher alcohols were performed using unrefined JO in a
microwave reactor. Typically, a glass vial was loaded with
JO (5 g, 20.0 mmol of C=C), alcohol (500 mmol), and
catalyst (2 mmol) and placed in the microwave reactor.
The mixture was stirred using a double-cross magnetic
stirrer (diameter *1 cm) for 30 s and subsequently heated
to the desired temperature in 2 min, and allowed to react
for 1 h. The content was cooled to room temperature,
washed three times with water and dried over MgSO4. The
remaining alcohol distilled of under reduced pressure, at a
temperature slightly below the boiling temperature of the
(Trans-) Esterification Reactions of Triolein, Methyl
Oleate, and Oleic Acid with Alcohols Using Metal Triflate
Catalysts
Catalyst-screening studies were performed using triolein
and oleic acid and the appropriate alcohol in glass
ampoules using conventional heating. A representative
example for methyl oleate and methanol is as follows: the
ampoule was loaded with methyl oleate (0.15 g,
0.5 mmol), methanol (1.01 mL, 25 mmol), and catalyst
(0.05 mmol). The ampoule was subsequently sealed using
a torch and placed in a preheated oven at a pre-determined
temperature. After a pre-determined reaction time, the
ampoule was taken from the oven and quenched by step-
wise submersion in water at 90 °C and water at 20 °C. For
safety reasons, particularly for reactions with gas phase
formation, the ampoule was subsequently submerged in
liquid nitrogen and opened. The liquid product was col-
lected, washed with water, dried over MgSO4, and ana-
alcohol used. The product was analysed by H and 13C
1
NMR and GC–MS.
Methoxy Methyl Esters of JO, 2 1H NMR (400 MHz,
CDCl3) d 5.34 (m, –CH=CH–), 3.65 (s, COOCH3, methyl
ester), 3.31 (s, CH–O–CH3, methoxy), 3.10 (m, CH–O–
CH3, methoxy), 2.76 (t, J = 6.1 Hz, =CH–CH2–CH=),
2.29 (t, J = 7.5 Hz, –CH2COO–), 2.10–1.00 (m, –CH2–),
0.87 (t, J = 7.1 Hz, –CH3). 13C NMR (50 MHz, CDCl3) d
178.1 (C=O, lactone), 174.2 (–COO–), 129.9–127.9
(CH=CH), 81.0 (–CH–, lactone), 56.3 (CH–O–CH3,
methoxy), 51.4 (COOCH3, methyl ester), 33.9–22.6 (m,
–CH2–), 14.0 (–CH3, end group). Isolated yield: 5.01 g
(95 wt% of theoretical yield).
1
lysed by H and 13C NMR and GC–MS.
Elemental analysis, calculated: C 76.5 %, H 12.1 %.
Found: C 76.5 %, H 12.2 %.
For triolein, the ampoule was loaded with triolein
(0.31 g, 0.35 mmol), methanol (0.7 mL, 17.5 mmol) and
catalyst (0.035 mmol). The reactions were performed in a
similar way as for methyl oleate.
Ethoxylated Ethyl Esters of JO, 3 1H NMR (400 MHz,
CDCl3) d 5.32 (m, –CH=CH–), 4.10 (dd, J = 14.2, 7.1 Hz,
COOCH2CH3, ethyl ester), 3.44 (m, CH–O–CH2CH3,
The methyl esters fraction in the mixture, gmethyl, and
the fraction of the methyl esters containing methoxy group
123

J Am Oil Chem Soc (2014) 91:325–336
329
ethoxy), 3.17 (m, CH–O–CH2CH3, ethoxy), 2.74 (t,
J = 6.1 Hz, =CH–CH2–CH=), 2.26 (t, J = 7.5 Hz,
–CH2COO–), 2.09–0.93 (m, –CH2–), 0.85 (t, J = 5.2 Hz,
CH3). 13C NMR (50 MHz, CDCl3) d 178.3 (C=O, lactone),
173.8 (–COO–), 130.2–127.7 (CH=CH), 79.3 (–CH–, lac-
tone), 64.0 (CH–O–CH2CH3, ethoxy), 60.1 (COOCH2CH3,
ethyl ester), 36.7–19.6 (–CH2–), 15.6 (CH–O–CH2CH3,
ethoxy), 14.4–13.9 (CH2CH3, end group and ethyl ester).
Isolated yield: 5.23 g (94 wt% of theoretical yield).
Elemental analysis, calculated: C 77.0 %, H 12.2 %.
Found: C 76.7 %, H 12.2 %.
J = 6.8 Hz, COO–CH2CH(CH3)2, isobutyl ester),
3.25–2.99 (m, CH–O–CH2–CH–(CH3)2, isobutoxy), 2.74
(t, J = 6.2 Hz, =CH–CH2–CH=), 2.28 (t, J = 7.6 Hz,
–CH2COO–), 2.00 (m, COO–CH2CH(CH3)2, isobutyl
ester) 1.95–1.03 (m, –CH2–), 0.92 (s, COO–CH2CH
(CH3)2, isobutyl ester), 0.90 (s, COO–CH2CH(CH3)2,
isobutyl ester), 0.86 (t, J = 6.0 Hz, CH3, end group). 13C
NMR (50 MHz, CDCl3) d 178.9 (C=O, lactone), 173.82
(–COO–), 132.8–125.2 (–CH=CH–), 79.5 (–CH–, lactone),
75.9 (CH–O–CH2–CH–(CH3)2, isobutoxy), 70.3 (COO–
CH2CH(CH3)2, isobutyl ester), 36.44–21.90 (–CH2–), 19.5
(CH–O–CH2–CH–(CH3)2, isobutoxy), 19.0 (COO–CH2
CH(CH3)2, isobutyl ester), 14.0 (CH3, end group). Isolated
yield: 5.64 g (94 wt% of theoretical yield).
Propoxylated Propyl Esters of JO, 4 1H NMR (400 MHz,
CDCl3) d 5.42–5.17 (m, –CH=CH–), 3.95 (t, J = 6.7 Hz,
COOCH2CH2CH3, propyl ester), 3.47–3.27 (m, CH–O–
CH2CH2CH3, propoxy), 3.16 (m, CH–O–CH2CH2CH3,
propoxy), 2.74 (t, J = 6.2 Hz, =CH–CH2–CH=), 2.37–2.16
(t, J = 7.5 Hz, –CH2COO–), 2.10–1.03 (m, –CH2–), 0.91 (t,
J = 7.5 Hz, COOCH2CH2CH3, propyl ester), 0.86 (m, CH3,
end group and propoxy). 13C NMR (50 MHz, CDCl3) d 177.7
(C=O, lactone), 173.8 (–COO–), 132.1–126.5 (CH=CH), 79.4
(–CH–, lactone), 70.6 (CH–O–CH2CH2CH3, propoxy), 65.7
(COOCH2CH2CH3, propyl ester), 35.8–20.5 (–CH2–), 14.0
(CH3, end group), 10.7 (CH–O–CH2CH2CH3, propoxy), 10.3
(COOCH2CH2CH3, propyl ester). Isolated yield: 5.52 g
(95 wt% of theoretical yield).
Elemental analysis, calculated: C 77.5 %, H 12.4 %.
Found: C 77.2 %, H 12.4 %.
Results and Discussion
Model Studies on the Trans-Esterification of Triolein
with Methanol using Metal Triflate Catalysts
The potential of metal triflate catalysts for (trans)-esterifi-
cation reactions with higher alcohols was assessed by
performing model studies with a system consisting of tri-
olein and methanol (165 °C, 1 h, methanol to triolein
molar ratio of 50) using conventional heating, see
Scheme 1.
Elemental analysis, calculated: C 77.5 %, H 12.3 %.
Found: C 76.8 %, H 12.3 %.
Iso-Propyl Esters of JO, 5 1H NMR (400 MHz, CDCl3) d
5.43–5.23 (m, –CH=CH–), 4.99 (m, CH(CH3)2, isopropyl
ester), 2.75 (t, J = 6.1 Hz, =CH–CH2–CH=), 2.32 (t, J =
7.4 Hz, –CH2COO–), 2.24 (t, J = 7.5 Hz, –CH2COO–),
2.09–0.98 (m, –CH2–), 0.86 (t, J = 5.4 Hz, CH3, end
group). 13C NMR (50 MHz, CDCl3) d 178.9 (C=O, lac-
tone), 173.4 (–COO–), 131.10–125.49 (CH=CH), 67.26
(CH(CH3)2, isopropyl ester), 35.1–22.2 (–CH2–), 21.8
(CH(CH3)2, isopropyl ester), 14.0 (CH3, end group). Iso-
lated yield: 5.37 g (93 wt% of theoretical yield).
Six metal triflate catalysts were tested, viz., scandium,
bismuth, zinc, aluminium, copper, and lanthanum triflate.
In addition, aluminium chloride was used as well. The
conversion of the triolein to methyloleate was determined
1
using H NMR by monitoring the disappearance of char-
acteristic peaks of the glycerol backbone at d 5.26 and
4.0–4.35 ppm, and the appearance of a characteristic
methyl ester peak at d 3.6 ppm. The results of the catalyst-
screening study are presented in Table 2.
Sc(OTF)3, Bi(OTf)3, and Al(OTf)3 were the most active
in the series and gave[95 % conversion of the triolein; the
other triflates were less active. The conversion using AlCl3
was considerably lower than with Al(OTf)3 (7 vs 99 %),
indicating that the anion plays a role in the reaction
mechanism and affects reaction rates. The major product is
Elemental analysis, calculated: C 77.7 %, H 12.3 %.
Found: C 76.9 %, H 12.3 %.
Iso-Butoxylated iso-Butyl Esters of JO, 6 1H NMR
(400 MHz, CDCl3) d 5.43–5.12 (m, –CH=CH–), 3.75 (d,
Scheme 1 Reaction products
for the trans-esterification of
triolein with alcohols using
metal triflate catalysts
123

330
J Am Oil Chem Soc (2014) 91:325–336
methyl oleate, as confirmed by H and 13C NMR spectra.
1H NMR spectra of the products also showed a reduction of
the intensity of the characteristic peaks of the C=C bonds at
d 5.29 ppm and the appearance of new peaks at d 3.26 ppm
(singlet) and d 3.08 ppm (multiplet). Apparently, the C=C
double bond is reactive under these conditions. A possible
side reaction is methanol addition to the C=C bond to form
an ether group (alkoxylation, see Scheme 1). Alkoxylation
has also been reported by Madrigal [16] for the H2SO4-
catalysed reaction of soybean oil with alcohols at
100–140 °C. Besides the esters, 18–31 % of the C=C unit
was alkoxylated. In a more recent study, Moreau [17] and
Pioch [18] described that (partly) methoxy methyl stearate
was obtained when methyl oleate or oleic acid was reacted
with methanol with dealuminated H-Y faujasites catalyst at
150–190 °C. Related reactivity has also been disclosed for
the hydration of 1-phenyl-1-propyne in water using
Sc(OTf)3, In(OTf)3, and Yb(OTf)3 at 150–225 °C [19].
GC–MS analysis was applied to confirm the presence of
methyl ether branches in the fatty acid chain. Two isomers
were identified, i.e., methyl 9- and 10-methoxy octadeca-
noate with mass fragmentation patterns in line with those
reported in the literature [17, 20]. The extent of methoxy-
1
1
lation was determined using H NMR data and the results
are shown in Fig. 2. Clearly, full conversion of the C=C
bond was not observed and the maximum fraction of
methoxy group was less than 15 % and depending on the
metal triflate catalyst. Highest amounts of methoxy groups
were observed for the Bi(OTf)3 and Al(OTf)3.
The introduction of branches on the fatty acid chain by
an alkoxylation reaction may also have a beneficial effect
on the cold-flow properties of the product [16, 21, 22].
Therefore, the effect of process conditions on the Al(OTf)3
catalysed alkoxylation with methanol was investigated
with the primary objective to maximise the amount of
methoxy branches. For this purpose, the extent of meth-
oxylation was studied by performing reactions using
methyl oleate and methanol as model compounds. The
reaction time, molar excess of methanol to methyl oleate
and catalyst loading were varied. The fraction of the
methoxy groups versus time at different molar excesses of
methanol is shown at Fig. 3.
Table 2 Results of the catalyst-screening study on the trans-esteri-
fication of triolein with methanol
The fraction of methoxy groups versus time shows a
clear maximum at about 2–3 h reaction time. The maxi-
mum fraction was about 18 mol% for the highest methanol
to methyl oleate ratio. At prolonged reaction times, the
fractions of the methoxy product are lowered to about
5 mol%. This finding is not in agreement with the meth-
oxylation of methyl oleate using solid dealuminated Y
faujasites catalysts [17, 18]. Here, the fraction of methoxy
products remained constant at a level between 40 and 50 %
after prolonged reaction times, indicative for an equilib-
rium reaction. A possible explanation is the occurrence of
other methanol consuming reactions (e.g., etherification,
vide infra) catalysed by the metal triflates, driving the
equilibrium to the side of the starting material. Further
Entry
Catalyst
Conversion
(mol%)
1
2
3
4
5
6
7
Sc(OTf)3
Bi(OTf)3
La(OTf)3
Cu(OTf)2
Al(OTf)3
Zn(OTf)2
AlCl3ꢀ6H2O
96
98
56
92
99
65
7
1
1
2
1
1
2
2
The conversion is the average values of at least two experiments.
Reaction conditions: 165 °C, conventional heating, 1 h, catalyst
intake: 10 mol% to triolein, 50 fold molar excess of MeOH
Fig. 2 Catalyst-screening study
on the trans-esterification and
alkoxylation of triolein with
methanol (165 °C, conventional
heating, 1 h, 10 mol% catalyst
intake on triolein, 50 fold molar
excess of MeOH)
123

J Am Oil Chem Soc (2014) 91:325–336
331
Model Studies on the Esterification of Oleic Acid
with Methanol Using Metal Triflate Catalysts
detailed studies will be required to draw definite
conclusions.
Higher catalyst intakes also did not lead to higher
fractions of the methoxy products. Using a 50 mol% cat-
alyst loading and a 50 times molar excess MeOH, 16 mol%
methoxy product after 1 h reaction time was obtained,
which is similar to the value obtained at lower intakes.
After 24 h, the amount was reduced to 5 mol%.
A second series of catalytic reactions using metal triflate
catalysts were carried out with a free fatty acid (oleic acid)
instead of the triolein (Scheme 3). The reactions were
performed at two temperatures (135 and 165 °C) using
conventional heating. 1H NMR spectra of the reaction
product showed quantitative conversion of the free fatty
acid to the methyl ester at both temperatures using all
catalysts. We selected Al(OTf)3 for further studies as it is
the most active catalyst and non-toxic. The triolein con-
version for the trans-esterification reaction with methanol
(vide supra) were not quantitative at 165 °C. Apparently,
the esterification reaction is much faster than the trans-
esterification reaction at these conditions, which is in line
with literature data in the (trans-) esterification of triolein
and oleic acid with Sc(OTf)3 and Bi(OTf)3 [11]. Alkoxy-
lation also occurred, with methoxy fractions in the range as
observed for the trans-esterification reaction of triolein
with methanol.
The alkoxylation reaction with methanol was also per-
formed with methyl linoleate instead of methyl oleate.
With Al(OTf)3 at 165 °C, partial methoxylation of the C=C
bonds occurred and an isomeric mixture of mono-methoxy
and di-methoxy methyl stearate was obtained (Scheme 2).
The presence of these compounds was confirmed by GC–
MS analyses. Clear GC peaks with characteristic mass
fragmentation patterns in line with literature data [23] were
observed for methyl- 9(10),12(13)-dimethoxyoctadecano-
ate, methyl 9(10)-methoxy-12(13)-octadecenoate, and
methyl- 12(13)-methoxy-9(10)-octadecenoate.
13C NMR spectra of the product show, next to the
characteristic peak of the methoxy ester group at d
56.3 ppm, small peaks at d 177.2 and d 80.9 ppm. A
possible side reaction is the isomerisation–lactonisation of
free fatty acids (Scheme 3). Characteristic peaks of the
1
lactones were not clearly observed in H NMR spectra of
the products due to overlap with other peaks, and this
hampers quantification of the amount of lactones formed.
Based on available 13C NMR data [24], the peaks at d
177.2 and d 80.9 ppm are indicative for the formation of
the c-lactone instead of the d-lactone.
The lactonisation of unsaturated fatty acids using metal
triflates has been reported in the literature. Gooben and co-
workers [25] reported that AgOTf, Bi(OTF)3, In(OTf)2,
and Cu(OTf)2 catalysts are active catalysts for the
Fig. 3 Methoxylation of C=C bonds versus time at different meth-
anol ratios for the alkoxylation of methyl oleate with methanol using
Al(OTf)3 (trendlines are for illustrative purpose only, 165 °C,
conventional heating)
Scheme 2 Methoxylation of methyl linoleate using Al(OTf)3 catalyst
123

332
J Am Oil Chem Soc (2014) 91:325–336
Scheme 3 Esterification and
lactonisation of oleic acid by
metal triflate catalysts
Alkoxylation was not observed for i-PrOH, the only sec-
ondary alcohol in the series, presumably for steric/elec-
tronic reasons. Similar results were reported for the trans-
esterification and alkoxylation reaction of soybean oil with
i-PrOH using H2SO4 as the catalyst (140 °C, 19 h) [16].
It is well-known that the rates of trans-esterification
reactions are highly dependent on the molecular structure
of the alcohols. Primary alcohols are the most reactive,
followed by secondary alcohol, and the least reactive are
tertiary alcohols [26]. As such, it is also not surprising that
t-BuOH was not reactive under these reaction conditions.
Possible byproducts when using higher alcohols are
olefins and ethers by the dehydration/addition reaction
(Scheme 4) [27]. To assess the occurrence of these reac-
tions, i-PrOH and the Al(OTf)3 catalyst were allowed to
react at standard reaction conditions (185 °C, 1 h). The
gaseous products were collected and analysed using GC–
MS. Both propylene and di-isopropyl ether were detected,
proof for the occurrence of dehydration and etherification
reaction.
Fig. 4 Fractions of esters and alkoxylated products for the reaction of
methyl oleate with higher alcohols using Al(OTf)3 as the catalyst
(10 mol% catalyst, 50 fold molar excess of alcohol, 185 °C,
conventional heating, 1 h)
isomerisation-lactonisation of 10-undecenoic acid to the
corresponding c-lactone. The highest yield (50 %) was
obtained at 160 °C using 5 mol% of the AgOTf catalyst.
The isomerisation-lactonisation of internal unsaturated
fatty acids with 9, 13, and 18 carbon chains using AgOTf at
130 °C gave c-lactones in isolated yields between 51 and
72 % (24 h, chlorobenzene) [25]. Cermak and Isbell [24]
reviewed methods for the isomerisation–lactonisation of
unsaturated fatty acids to give d- and c-lactone using sul-
phuric acid in stoichiometric or super stoichiometric
amounts. At low temperatures (\20 °C), the major pro-
ducts were d-lactones, while c-lactones were the major
products at moderate temperatures (50–150 °C).
Trans-Esterification Reactions of JO with Alcohols
Using Al(OTf)3 as the Catalyst
JO Characterisation
The fatty acid composition of the JO used for this study
was determined using GC–MS, and the results are given in
Table 3. The composition of JO used in this study is close
to that reported in the literature with a very slight differ-
ence in the amount of palmitic acid. The total amount of
unsaturated fatty acids in the JO used in this study is
82.9 wt%. The acid value was determined by titration and
found to be 4.2 mg KOH/g oil, corresponding with a FFA
content of 2.1 wt% (as oleic acid), indicating that the oil
contains significant amounts of free fatty acids.
Model Studies on the Trans-Esterification of Methyl
Oleate with Higher Alcohols Using Al(OTf)3
The trans-esterification of methyl oleate with higher alco-
hols (EtOH, n-PrOH, i-PrOH, i-BuOH, t-BuOH) was
studied with Al(OTf)3, one of the most active catalysts for
the reaction of triolein with methanol using conventional
heating (Fig. 2). For all alcohols, except t-BuOH, quanti-
tative trans-esterification and the formation of the ester of
the higher alcohol were observed in 1 h at 165 °C.
Alkoxylation of the C=C bond in the fatty ester also
occurred to a significant extent for EtOH, n-PrOH, and i-
BuOH, though the maximum fraction of the alkoxylated
ester was again low (\10 %), see Fig. 4 for details.
Preparative Reactions of JO with Higher Alcohols
Preparative reactions of JO with methanol and various
higher alcohols (EtOH, n-PrOH, i-PrOH, i-BuOH, t-BuOH)
using Al(OTf)3 were performed in a microwave reactor
(T = 165 or 180 °C, catalyst intake of 10 mol%, 25 fold
molar excess of alcohol, 1 h). After reactions, the esters
123

J Am Oil Chem Soc (2014) 91:325–336
333
Scheme 4 Possible reaction
pathways for the dehydration
and etherification of primary,
secondary and tertiary alcohols
[27–29]
Table 3 Fatty acid composition of the crude JO used in this study
Fatty acid
This study
Literature
(wt%) [30]
(wt%)
(GC-FID)
(mol%)
Palmitoleic acid
Palmitic acid
C16:1
0.9
1.0
12.7
43.5
37.6
5.2
0–1.3
14.1–15.3
29.0–4.2
34.3–45.8
3.7–9.8
C16:0 11.7
C18:2 43.8
C18:1 38.2
Linoleic acid
Oleic acid
Stearic acid
C18:0
5.3
Total unsaturated acids
82.9
82.1
63.4–91.3
were obtained as yellow liquids in[93 wt% isolated yield
and analysed by 1H and 13C NMR and elemental analyses.
An overview of the results is given in Table 5. t-BuOH was
not reactive, a result in line with the model component
study. The reaction with i-PrOH was carried out at 135 °C.
At higher temperatures, the pressure exceeded the maxi-
mum pressure in the microwave reactor due to the forma-
tion of a gas phase component like propylene by the
catalytic decomposition of i-PrOH (vide supra).
The FFA value of the products ranged between 0.05 and
0.06 (wt%), and this value is considerably lower than the
JO feed (2.1 wt%). This indicates that both trans-esterifi-
cation of the triglycerides and esterification of the free fatty
acids occurred, in line with the model component studies.
1H NMR spectra of the products (Fig. 5) and 13C NMR
show the presence of the ester and alkoxy groups (Table 4).
The extent of alkoxylation was in line with the model
component studies, and the highest fraction was obtained
using i-BuOH (Table 5). In addition, small amounts of
c-lactones were detected in 13C NMR spectra, though they
could not be quantified.
Fig. 5 1H NMR spectra of JO and derivatives
The viscosity of the JO feed and the higher alcohol esters
derived thereof are provided in Table 6. As expected, the
viscosity of the esters is considerably lower than that of the
original JO. The ester substituent affects the viscosity and
the viscosity increases with the number of carbon atoms in
the alcohol, viz., 5.76 for MeOH to 8.26 mPa.s for
i-BuOH. The synthetic methodology described here leads
to partial alkoxylation of the C=C of the fatty acids chains.
To check whether these branches affect the viscosity of the
product, the viscosity of the JO methyl ester (2) was
compared with a JO methyl ester (1) prepared by a standard
Properties of the JO Derivatives
Relevant physical properties of the JO ester derivatives
with an emphasis on cold-flow properties were determined.
123

334
J Am Oil Chem Soc (2014) 91:325–336
Table 4 Summary of characteristic peaks for products of the reaction of JO with higher alcohols
Alcohol
Ester group (ppm)
1H NMR
Alkoxy group (ppm)
1H NMR
Lactone group
(ppm)
13C NMR
13C NMR
13C NMR
MeOH
EtOH
3.65 (CH3)
51.4 (CH3)
3.31 (CH3), 3.10 (CH)
56.3 (CH3)
178.3 (C=O),
81.0 (CH)
4.10 (CH2)
60.1 (CH2)
3.44 (CH2), 3.17 (CH)
64.0 (CH2)
178.3 (C=O),
79.3 (CH)
n-PrOH
3.95 (OCH2), 0.91 (CH3)
4.99 (CH)
65.7 (OCH2), 10.3 (CH3)
67.3 (CH), 21.8 (CH3)2
3.47–3.27 (OCH2-), 3.16
(CHO), 0.86 (CH3),
70.6 (OCH2), 10.7 (CH3)
177.7 (C=O),
79.4 (CH)
i-PrOH
i-BuOH
–
–
178.9 (C=O)
3.75 (OCH2), 2.00 (CH),
0.92 and 0.90 (CH3)2
70.3 (OCH2), 19.0
(CH3)2
3.25–2.99 (CHOCH2)
75.9 (CHOCH2), 19.5
(CH3)
176.9 (C=O),
79.5 (CH),
Table 5 Overview of results for the reaction of JO with higher alcohols using Al(OTf)3 as the catalyst
Compound
Alcohol
galkyl (mol%)
galkoxy (mol%)
Final acid value
(mg KOH/
g oil)
Methoxy methyl esters of JO (2)
Ethoxylated ethyl esters of JO (3)
Propoxylated propyl esters of JO (4)
Iso-propyl esters of JO (5)
Iso-butoxylated iso-butyl esters of JO (6)
–
MeOHa
EtOHb
n-PrOHb
i-PrOHc
i-BuOHb
t-BuOHd
98
98
98
97
98
1
1
1
2
1
0
11
9
2
2
1
0
3
0
0.10
0.11
0.11
0.13
0.12
n.d.
8
21
Values are average values of two duplicate experiments. Reaction conditions: 259 molar excess of alcohol, catalyst loading: 10 mol% to C=C
n.d. not determined
a
At 165 °C
At 180 °C
b
c
Reaction temperature 145 °C due to pressure safety limit of reactor (21 bars)
135 °C due to pressure safety limit of reactor (21 bars)
d
Table 6 Dynamic viscosity of JO and derivatives at 40 °C
The cold-flow properties of the JO and higher alcohol
derivatives were determined and the results are given in
Fig. 6. The CP and PP of JO were -2 and -3 °C,
respectively, and these values are in line with literature
data (CP of 2 °C [31] and PP of -3 °C [31, 32]). The PP is
in the expected range for plant oils, see Fig. 1, with higher
levels of unsaturation leading to lower PP values.
Compound
Alcohol Viscosity
(910-3 Pa s)
JO
–
34.06
Methyl esters of JO (1)
MeOHa
MeOHb
EtOH
n-PrOH
i-PrOH
4.47
5.76
6.93
7.66
8.20
8.26
Methoxy methyl esters of JO (2)
Ethoxylated ethyl esters of JO (3)
Propoxylated propyl esters of JO (4)
Iso-propyl esters of JO (5)
The CP and PP of the methyl esters of JO, 1, were 0 and
1 °C, respectively. These values are slightly higher than for
JO. Apparently, the trans-esterification reaction with
methanol does not have a significant effect on cold-flow
properties, though it considerably lowers the viscosity (vide
supra). PP and CP values for several plant oils and methyl
esters derived thereof are given in Table 7. It shows that in
general the CP is increased upon trans-esterification while
an opposite effect is observed for the PP.
Iso-butoxylated iso-butyl esters of JO (6) i-BuOH
a
Prepared using a standard base catalysed trans-esterification of JO
with methanol
b
Prepared using the synthetic methodology described in this paper;
product contains -OMe groups in fatty acid chain
For comparison, the PP and CP of pure triolein (7) and
methyl oleate (8) were determined. The CP/PP of triolein
and methyl oleate are in the same range, -23/-26 and
-24/-30 °C, respectively. The values for methyl oleate
base catalysed trans-esterification of JO with methanol.
The viscosity of 2 is a factor 1.3 higher than that of 1, an
indication that the presence of methoxy branches slightly
increases the viscosity.
123

J Am Oil Chem Soc (2014) 91:325–336
335
Fig. 6 Cold-flow properties of
JO and derivatives
Table 7 Cold-flow properties
of PPO and their alkyl esters
Plant
CP/PP values
Oil
Mol ratio unsaturated/
saturated chains
Average
chain length
References
[33]
Methyl ester
1
2
3
4
5
6
Castor
4.0/-15.0
3.0/-8.0
7.0/-25.0
5.0/-12.0
10.0/-6.0
-2.0/-9.0
2.0/-1.0
97.0/3.0
79.3/20.7
69.4/30.5
94.0/6.0
89.5/10.5
92.0/8.0
18.0
17.8
18.2
17.9
17.9
17.9
Pumpkin
Groundnut
Rapeseed
Soybean
Sunflower
8.0/-3.0
-3.9/-31.7
-3.9/-12.2
7.2/-15.0
[34]
0.0/-4.0
are much lower than for the JO methoxy methyl esters (2),
likely caused by the saturated fatty ester fraction in the JO
methoxy methyl esters, which is known to most prone to
crystallisation. Support for this statement was obtained by
measuring the PP and CP of methyl stearate (10) and
mixtures of methyl stearate and methyl oleate (1–1 wt
ratio, 11). Methyl oleate has a CP and PP of -24 and
-30 °C, while the values for methyl stearate are much
higher and are 36 and 34 °C, respectively (see Fig. 6). The
mixture 11 gave a CP and PP of 28 °C, close to those of
methyl stearate. Thus, the cold-flow properties of fatty acid
methyl esters are affected heavily by the amount of satu-
rated fatty acid chains.
additional branches. Thus, the effect of OMe branches on
cold-flow properties is limited, which could be due to the
relatively low amounts of the methoxy groups (vide supra).
A number of JO esters with different alcohols were
prepared and this allows an assessment of the effect of the
size of the JO ester group on cold-flow properties. When
considering the primary alcohols in the series (MeOH,
EtOH, n-PrOH, i-BuOH), the C4 alcohol in the series (6)
give the lowest PP and CP, viz -10, and -15 °C versus
-1 and -1 °C for the methyl ester 2. Thus, the cold-flow
properties are considerably improved by using higher
alcohols for the esterification reaction. The lowest values
for the CP and PP were obtained for the secondary alcohol
in the series (i-PrOH, 5), -3 and -24 °C, respectively.
Thus, not only the number of carbon atoms in the alcohol
but also the position of the substituents on the ester group
plays a role.
The synthetic methodology reported in this paper for the
synthesis of the methyl ester of JO results, besides the
introduction of ester groups, also applies to the introduction
of methoxy groups (-OMe) on the fatty acid chain by
methoxylation of the C=C bonds. The effect of these
additional branches on the PP and CP was probed by
comparing the values with that of the JO methyl esters (1)
prepared using standard base catalysed methodology. The
PP and CP of the methyl ester with -OMe ether groups (2)
are 1–2 °C lower than the methyl ester without these
Conclusions
Metal triflates were shown to be active catalysts for the
simultaneous trans-esterification of the triglycerides and
123

336
J Am Oil Chem Soc (2014) 91:325–336
13. Haraldsson G (1983) Degumming, dewaxing, and refining. J Am
Oil Chem Soc 60:251–256
14. Daniel L, Ardiyanti AR, Schuur B, Manurung R, Broekhuis AA,
Heeres HJ (2011) Synthesis and properties of highly branched
Jatropha curcas L. oil derivatives. Eur J Lipid Sci Technol
113:18–30
15. Reklaitis GV (1983) Introduction to material and energy bal-
ances. Wiley, Canada
16. Madrigal RV, Bagby MO, Pryde EH (1988) The acid-catalyzed
addition of alkoxyl groups to the olefinic double bonds of soy-
bean oil. J Am Oil Chem Soc 65:1508–1510
17. Lansalot-Matras C, Lozano P, Pioch D, Finiels A, Moreau C,
Claude S (2006) Methoxylation of methyl oleate in the presence
of dealuminated Y faujasites in their protonic form. J Am Oil
Chem Soc 83:725–729
18. Pioch D, Nguyen AT, Lansalot-Matras C, Finiels A, Moreau C
(2010) Proceeding of the 3rd Workshop on Fats and Oils as
Renewable Feedstock for the Chemical Industry, Emden, Germany
19. Rebacz NA, Savage PE (2010) Hydration of 1-phenyl-1-propyne
in high-temperature water with catalysis by water-tolerant Lewis
acids. Ind Eng Chem Res 49:535–540
the esterification of the FFA in JO with various alcohols.
Besides (trans)-esterification, partial alkoxylation of the
carbon–carbon double bonds in the fatty acid chain, and to
a lesser extent, isomerisation-c-lactonisation of the free
unsaturated fatty acids in the oil occurred. Aluminium
triflate was found to be the most active catalyst, next to
bismuth triflate and scandium triflate. Quantitative yields
were obtained for the trans-esterification reaction when
using primary and secondary alcohols, whereas a tertiary
alcohol like t-BuOH was not reactive. Alkoxylation of the
carbon–carbon double bonds was accomplished exclu-
sively for primary alcohols, with higher alcohols being
more reactive. Cold-flow properties of the Jatropha oil
derivatives were determined and best results were obtained
for the iso-propyl esters of JO, with CP and PP values of
-3 and -24 °C, respectively.
20. Gunstone FD, Inglis RP (1973) Application of the oxymercura-
tion–demercuration raction to long-chain unsaturated esters.
Chem Phys Lipids 10:73–88
21. Smith PC, Ngothai Y, Nguyen QD, O’Neill BK (2010) The
addition of alkoxy side-chains to biodiesel and the impact on flow
properties. Fuel 89:3517–3522
Acknowledgments The authors would like to thank J. van der
Velde for performing elemental analysis and the Royal Netherlands
Academy of Arts and Sciences (KNAW) for the financial support
(Project SPIN 05-PP-18).
22. Smith PC, O’Neill BK, Ngothai Y, Nguyen QD (2009) Butoxy-
lation of butyl biodiesel: reaction conditions and cloud point
impact. Energ Fuel 23:3798–3803
References
´
´
23. Carballeira NM, Gonzalez MV, Pagan M (1997) Neighboring
methoxyl participation in the acid catalyzed methoxylation of
methylene-interrupted fatty acids. Chem Phys Lipids 89:91–96
24. Cermak SC, Isbell TA (2000) Synthesis of d-stearolactone from
oleic acid. J Am Oil Chem Soc 77:243–248
1. National Biodiesel Board (2012) Biodiesel production breaks
record with 1 billion gallons produced in 2011. http://www.
oemoffhighway.com/news/10619617/biodiesel-production-breaks-
record-with-1-billion-gallons-produced-in-2011. Accessed 9 March
2012
25. Gooßen LJ, Ohlmann DM, Dierker M (2010) Silver triflate-cat-
alysed synthesis of c-lactones from fatty acids. Green Chem
12:197–200
26. Ramalinga K, Vijayalakshmi P, Kaimal TNB (2002) A mild and
efficient method for esterification and transesterification cata-
lyzed by iodine. Tetrahedron Lett 43:879–882
27. Bedia J, Barrinuevo R, Rodriguez-Mirasol J, Cordero T (2011)
Ethanol dehydration to ethylene on acid carbon catalysts. Appl
Catal B: Environ 103:302–310
28. Araujo AS, Souza MJB, Fernandes VJ Jr, Diniz JC (1999) Kinetic
study of isopropanol dehydration over silicoaluminophosphate
catalyst. React Kinet Catal Lett 66:141–146
29. Gates BC, Wisnouskas JS, Heath HW Jr (1972) The dehydration
of t-butyl alcohol catalyzed by sulfonic acid resin. J Catal
24:320–327
30. Gu¨bitz GM, Mittelbach M, Trabi M (1999) Exploitation of the
tropical oil seed plant Jatropha curcas L. Bioresour Technol
67:73–82
31. Achten WMJ, Verchot L, Franken YJ, Mathijs E, Singh VP, Aerts
R, Muys B (2008) Jatropha bio-diesel production and use. Bio-
mass Bioenerg 32:1063–1084
2. Singh SP, Singh D (2010) Biodiesel production through the use of
different sources and characterization of oils and their esters as
the substitute of diesel: a review. Renew Sust Energ Rev
14:200–216
3. Dunn RO (2011) Improving the cold flow properties of biodiesel
by fractionation. In: Ng TB (ed) Soybean—applications and
technology. Intech, Rijeka, pp 213–214
4. Knothe G (2005) Dependence of biodiesel fuel properties on the
structure of fatty acid alkyl esters. Fuel Process Technol
86:1059–1070
5. Hoekman SK, Broch A, Robbins C, Ceniceros E, Natarajan M
(2012) Review of biodiesel composition, properties, and specifi-
cations. Renew Sustain Energ Rev 16:143–169
6. Knothe G (2009) Improving biodiesel fuel properties by modi-
fying fatty ester composition. Energ Environ Sci 2:759–766
7. Dunn RO (2009) Cold-flow properties of soybean oil fatty acid
monoalkyl ester admixtures. Energ Fuel 23:4082–4091
8. Smith PC, Ngothai Y, Nguyen QD, O’Neill BK (2010) Improving
the low-temperature properties of biodiesel: methods and con-
sequences. Renew Energ 35:1145–1151
9. Vyas AP, Verma JL, Subrahmanyam N (2010) A review on
FAME production processes. Fuel 89:1–9
10. Lotero E, Liu Y, Lopez DE, Suwannakarn K, Bruce DA, Good-
win JG Jr (2005) Synthesis of biodiesel via acid catalysis. Ind
Eng Chem Res 44:5353–5363
32. Forson FK, Oduro EK, Hammond-Donkoh E (2004) Performance
of jatropha oil blends in
29:1135–1145
a diesel engine. Renew Energ
33. Bello EI, Mogaji TS, Agge M (2010) The effects of transesteri-
fication on selected fuel properties of three vegetable oils. J Mech
Eng Res 3:218–225
34. Gunstone FD, Alander J, Erhan SZ, Sharma BK, McKeon TA,
Lin JT (2007) Nonfood uses of oils and fats. In: Gunstone FD,
Harwood JL, Dijkstra AJ (eds) The lipid handbook, 3rd edn. CRC
Press, Boca Raton
11. Socha AM, Sello JK (2010) Efficient conversion of triacylgly-
cerols and fatty acids to biodiesel in a microwave reactor using
metal triflate catalysts. Org Biomol Chem 8:4753–4756
12. Levine RB, Bollas AA, Durham MD, Savage PE (2012) Triflate-
catalyzed (trans-) esterification of lipids within carbonized algal
biomass. Bioresour Technol 111:222–229
123