An experimental investigation into methyl laureate production via direct esterification of solid fatty acid by using amylum sulfuric acid: An efficient, biodegradable, and recyclable solid acid catalyst

Article abstract of DOI:10.1007/s11164-014-1548-2

Recently, many processes have been reported to produce biodiesel via alkali-catalyzed transesterification of triglyceride molecules. However, this requires certain precautions. First, the triglyceride should be nearly pure. Studies show that the presence of water or free fatty acids acts as a poison for the catalyst. Second, the price of pure triglyceride does not allow biodiesel to compete with diesel fuel in cost. These disadvantages are the main reasons why researchers have recently focused on other feedstocks for biodiesel fuel production. Therefore, we investigated the chemical conversion of lauric acid and methanol to methyl laureate fuel via esterification reaction over amylum sulfuric acid as an efficient, biodegradable, and recyclable solid acid catalyst. Synthesized methyl laureate fuel was fittingly characterized by Fourier transform infrared spectroscopy as well as by ¹H and ¹³C nuclear magnetic resonance spectroscopic techniques.

Full text of DOI:10.1007/s11164-014-1548-2

Res Chem Intermed
DOI 10.1007/s11164-014-1548-2
An experimental investigation into methyl laureate
production via direct esterification of solid fatty acid
by using amylum sulfuric acid: an efficient,
biodegradable, and recyclable solid acid catalyst
Mehulkumar L. Savaliya Bharatkumar Z. Dholakiya
•
Received: 12 December 2013 / Accepted: 23 January 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Recently, many processes have been reported to produce biodiesel via
alkali-catalyzed transesterification of triglyceride molecules. However, this requires
certain precautions. First, the triglyceride should be nearly pure. Studies show that
the presence of water or free fatty acids acts as a poison for the catalyst. Second, the
price of pure triglyceride does not allow biodiesel to compete with diesel fuel in
cost. These disadvantages are the main reasons why researchers have recently
focused on other feedstocks for biodiesel fuel production. Therefore, we investi-
gated the chemical conversion of lauric acid and methanol to methyl laureate fuel
via esterification reaction over amylum sulfuric acid as an efficient, biodegradable,
and recyclable solid acid catalyst. Synthesized methyl laureate fuel was fittingly
1
13
characterized by Fourier transform infrared spectroscopy as well as by H and
nuclear magnetic resonance spectroscopic techniques.
C
Keywords Lauric acid Á Amylum sulfuric acid (ASA) Á Fatty acid Á Biodiesel Á
Esterification
Introduction
The depletion of fossil resources and environmental pollution are among the most
critical problems that threaten humanity. Attention is currently turned towards the
use of biomass or biomass-derived materials as replacements for petroleum fuel. In
1
893, Rudolf Diesel attempted to make use of peanut oil as fuel for diesel engines
M. L. Savaliya Á B. Z. Dholakiya (&)
Department of Applied Chemistry, S.V. National Institute of Technology, Ichchhanath,
Surat 395007, Gujarat, India
e-mail: bzd.svnit@gmail.com; bharat281173@gmail.com
M. L. Savaliya
e-mail: msmehulsavaliya@gmail.com
123

M. L. Savaliya, B. Z. Dholakiya
[
1]. Non-edible vegetable oils such as sea mango, castor, and Jatropha curcas oils
have been identified to be alternative feedstocks for biodiesel production [2]. These
oils are not suitable for human consumption because of the presence of some toxic
components. Among various non-edible oils, Jatropha oil is considered the most
suitable source of triglycerides for biodiesel production since its seed possesses high
oil content compared to other oils. It also has high productivity per hectare, which is
an important factor in selecting the most potential renewable source for biofuel. Its
composition has no significant differences from edible oils [3]. Biodiesel is
generally produced via transesterification of triglyceride molecules, in which one
molecule of triglyceride reacts with three molecules of alcohol in the presence of a
strong catalyst to produce three molecules of fatty acid alkyl esters and one
molecule of glycerol [4].
Usually, the actual amount of methanol used for transesterification is higher than
the stoichiometric amount in order to achieve acceptable conversions. For instance,
a methanol:oil molar ratio of 6:1 is a good choice for achieving 95 % conversion at
60 °C with 1 g of NaOH as a precursor of the sodium methoxide catalyst. Obtaining
such good results, however, requires certain precautions. First, the triglyceride
should be nearly pure. Studies show that the presence of water or free fatty acids
(
FFA) acts as poison for the catalyst. Second, the price of pure triglyceride does not
allow biodiesel to compete with diesel fuel in cost [5, 6]. These disadvantages are
the main reasons why researchers have recently focused on other feedstocks for
biodiesel production. Acid oils, which have high FFA content, are well known as
potential alternative raw materials. The presence of FFA requires the addition of a
pretreatment step before transesterification, in which FFAs react with methanol in
the presence of an acidic catalyst to produce biodiesel and water as shown in Fig. 1
[
7–12].
Amylum sulfuric acid (ASA) has also been used as a catalyst in numerous
organic reactions. As a heterogeneous catalyst, it is easily recovered from the
reaction media and can also be used for several repetitive cycles without significant
loss of activity. Amylum is a biodegradable polymer which contains numerous
hydroxyl functionalities. So, on chlorosulphonation of amylum, almost all hydroxyl
groups get converted into sulphonic acid groups. Therefore, it is able to give very
good acidity. Furthermore, these types of catalysts are efficient, environmentally
friendly, and biodegradable in nature. There are also some region-specific factors
influencing the choice of feedstocks for biodiesel production. Soybean oil is so far
the leading feedstock for production of biodiesel in the US [4]. Sunflower, canola,
palm, and cottonseed are the major biodiesel production sources in Brazil and India,
although they are producing edible oils, and in insufficient quantities even to fulfil
the domestic requirements. Considering this issue, edible oils cannot be utilized for
production of biodiesel in India. Thus, the raw materials which are presently
intended for biodiesel production in India are non-edible vegetable oils, such as
Jatropha curcas, Pongamia glabra pinnatta, Hevea brasiliensis, and Madhuca
indica. These are commonly found in the forests of India. In addition to the above
species, the identification of new feedstocks for biodiesel production has been
carried out with promising results [13].
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Direct esterification of solid fatty acid by using ASA
O
O
H
CH3
+
OH
H
3
C
OH
R
R
O
-
H O
2
Where R= Carbon chain in fatty acid molecule
Fig. 1 Esterification of FFAs and methanol to biodiesel
Experimental
General
All commercially available chemicals were purchased from Fluka and Merck, and
used without further purification. Fourier transform infrared spectroscopy (FT-IR)
spectrum was recorded on a FT-IR spectrophotometer (Model RZX; Perkin Elmer).
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13
H NMR and C NMR spectra were recorded in CDCl on a Bruker Advanced
3
DPX 400 MHz FT-NMR spectrometer using TMS as internal standard. Reaction
monitoring was accomplished by TLC on silica gel polygram SILG/UV 254 plates.
Materials and methods
Materials
Methanol and lauric acid used in the present study were purchased from Sterling lab
care, Surat, Gujarat, India.
Preparation of ASA catalyst
To a magnetically stirred mixture of amylum (5.00 g; Merck) in methylene
dichloride (20 mL), chlorosulfonic acid (1.00 g) was added dropwise at 0 °C during
2
h. After the addition was complete, the mixture was stirred for 2 h until the HCl
was removed from the reaction vessel. Then, the mixture was filtered and washed
with acetonitrile (30 mL) and dried at room temperature to obtain ASA as a white
powder (5.22 g). The sulfur content of the samples measured by conventional
?
elemental analysis was 0.55 mmol/g for ASA. The number of the H site of
amylum–SO H determined by acid–base titration was 0.50 meq/g. This value
3
corresponds to about 90 % of the sulfur content, indicating that most of the sulfur
species on the sample are in the form of the sulfonic acid groups. The general
reaction scheme for the synthesis of ASA is given in Fig. 2.
General procedure
ASA catalyzed esterification of lauric acid to methyl laureate
The lauric acid esterification process was usually carried out under continuous water
removal. Water removal during esterification is needed as it is formed as a side
123

M. L. Savaliya, B. Z. Dholakiya
CH OH
CH2OH
OH
CH2OH
2
O
O
O
OH
OH
O
O
OH
OH
OH
OH
OH
3
00-600
Amylum
Cl-SO H
3
-
HCl
0
-5 °C
CH OSO H
CH OSO H
CH2OSO3H
2
3
2
3
O
O
O
OSO H
OSO H
OSO3H
3
3
O
O
OSO H
HO SO
3
3
OSO H
OSO H
3
OSO H
3
3
3
00-600
Amylum Sulfuric Acid
Fig. 2 Reaction scheme for synthesis of ASA catalyst
product and will inhibit the activity of a solid acid catalyst. It can also promote a
reverse reaction. In addition, esterification is an equilibrium-limited reaction in
which full conversion can only be achieved when one of the products is removed. To
resolve this problem, anhydrous sodium sulfate (0.1 mol) was added in the reaction
to trap water formation. So, in the present study, In a three-necked round-bottom
flask (equipped with condenser, temperature indicator, and continuous water
removing system), a mixture of lauric acid (1 mol, 99 %), methanol (3 mol,
9
9.9 %), and ASA (0.3 g) was added and stirred at 65 °C for the appropriate time.
Completion of the reaction was indicated by TLC monitoring. Finally, the reaction
mixture was cooled to ambient temperature, and the ASA was filtered off. The filtrate
was poured into cold water to get methyl laureate at the upper layer. Furthermore,
unreacted lauric acid also tended to remain in the upper layer. So, it was filtered off
from the methyl laureate and a 92 % yield was obtained. The general reaction
scheme for esterification of lauric acid to methyl laureate is given in Fig. 3.
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Direct esterification of solid fatty acid by using ASA
O
O
H
CH
3
+
3CH
3
OH
O
OH
-
H O
2
Lauric acid
Methanol
Methyl laurate
Fig. 3 Esterification of lauric acid to methyl laureate
Plausible reaction mechanism pathway for ASA catalyzed esterification of lauric
acid to methyl laureate
The mechanism of the esterification reaction is proceed via four steps. In the first
step, protonation of lauric acid occurs to form protonated acid molecules by
liberation of proton from the ASA catalyst. In the second step, the positive charge of
protonated acid molecule gets transferred towards carbon to form carbocation and
the removal of water molecules takes place. In the third step, carbocation will get
attacked by the nucleophilic attack of methanol to form an intermediate compound.
In the fourth step, proton removal from the intermediate compound forms methyl
laureate. The general reaction mechanism scheme for esterification of lauric acid to
methyl laureate is given in Fig. 4 [14].
Results and discussion
The prepared solid acid catalyst was evaluated for the synthesis of methyl laureate
under reaction conditions of reaction temperature of 65 °C, stirring speed of
6
00 rpm, and 0.3 g catalyst. The best catalyst amount was chosen based on the yield
of maximum methyl laureate (92 %) with minimum unreacted methanol and lauric
acid content in the final product (methyl laureate). The synthesized catalyst was also
investigated for its recyclability. During the experiments, it was found that the
catalyst can be used for three repetitive cycles without significance loss of activity.
Fresh catalyst can give maximum conversion of lauric acid to methyl laureate up to
92 %. However its first, second, and third cycles can give maximum conversion up
to 90, 88, and 83 %, respectively.
1
H NMR characterization of synthesized methyl laureate
1
The use of H NMR analysis is convenient and fast in monitoring a reaction,
because a small aliquot can be extracted from the batch reaction at any given time,
1
and the H NMR spectrum analysis provides quantitative information pertaining to
the chemical species present in the reaction. The extent of esterification of lauric
1
acid was determined by H NMR spectroscopy. The purity of the methyl laureate
is further confirmed by the presence of peaks including 3.63 (q, 2H, –CH ), 3.55
2
(
m, 3H, –CH ), 2.32 (t, 2H, –CH –CO–O–), 1.31 [d, 15H, 8(–CH )], and 0.88 (s,
3 2 2
1
3
in Fig. 5.
H, –CO–O–CH ). The H NMR spectrum of synthesized methyl laureate is given
3
123

M. L. Savaliya, B. Z. Dholakiya
O
OH
+
H
O
OH2
-
2
H O
O
+
HO
CH3
C
O
C
O
CH3
H
+
-
H
O
C
O
CH3
Fig. 4 Reaction mechanism pathway for ASA catalyzed esterification of lauric acid to methyl laureate
1
3
C NMR characterization of synthesized methyl laureate
1
3
The progress of esterification of lauric acid was also determined by C NMR
spectroscopy. The purity of the methyl laureate is confirmed by the presence of
peaks including 172.68 (1C, CO), 63.11 (1C, –OCH ), 49.55 (1C, –CH –CO–O–),
3
2
1
3
3
synthesized methyl laureate is given in Fig. 6.
3.89–22.22 [9C, 9(–CH )], and 13.80 (1C, –CH ). The C NMR spectrum of
2 3
Reusability of catalyst
In order to reduce the cost of methyl laureate production, catalyst reusability is most
important, In this present study, the catalyst can be reused several times after simple
regeneration for esterification of lauric acid under identical reaction conditions. The
1
23

Direct esterification of solid fatty acid by using ASA
1
Fig. 5 H NMR spectrum of synthesized methyl laureate
1
Fig. 6 C NMR spectrum of synthesized methyl laureate
3
123

M. L. Savaliya, B. Z. Dholakiya
Fig. 7 FT-IR spectrum of fresh and spent catalyst
Fig. 8 Effect of catalyst cycle time on % conversion of lauric acid to methyl laureate
results clearly indicate that the catalyst can be reused for three times without
significance loss of activity. It has been found that amylum retains its structure
through the reaction without any change, and this is also clearly proven by spectral
characterization of the catalyst. Figure 7 shows the FT-IR spectrum of fresh and
spent catalyst.
1
23

Direct esterification of solid fatty acid by using ASA
-
1
The FT-IR spectrum of ASA is confirmed with the presence of 3,468.13 cm
-
1
-1
(
(
(
–OH stretching of phenolic –OH), 1,334.78 cm (C–O–H bending), 1,153.47 cm
SO asymmetric stretching provided by presence of SO H group), 1,003.02 cm
-
1
2
3
-
1
-1
SO symmetrical stretching), 925.86 cm (C–O–C stretching), 763.84 cm (C–C
2
-
1
stretching) ,and 709.83, 574.81, and 532.37 cm (skeleton modes of pyranol ring),
respectively.
However, little decrement in the methyl laureate production was observed in
subsequent runs. The observed catalyst deactivation could be due to the
modification of the catalyst structure or leaching of active sites at a given reaction
temperature. Catalyst reusability is shown in Fig. 8.
Conclusion
Esterification of lauric acid and methanol in the presence of ASA, a reusable solid
acid catalyst, was successfully conducted. During the esterification reaction, it has
been found that the process was very convenient and efficient. Also, the synthesized
catalyst can be used for three repetitive cycles without significance loss of activity.
Furthermore, the world is facing the problem of an abundance of feedstocks for
biodiesel synthesis. In addition, the price of pure triglyceride does not allow
biodiesel to compete with diesel fuel in cost. So, such avenues could be followed as
being efficient for biodiesel synthesis from free fatty acid esterification. The method
offers a marked improvement with its operational simplicity, low reaction time, and
high yields of pure product. Recently, one of the major hurdles towards widespread
commercialization of biodiesel has been the abundance of feedstocks. Therefore, by
applying such strategies, one can easily produce biodiesel fuel in an effective
manner.
Acknowledgments The authors are very grateful to the Department of Applied Chemistry, Sardar
Vallabhbhai National Institute of Technology (SVNIT), Surat, for providing laboratory facilities and
financial support for the course of this work. For characterization, we are grateful to Mr. Avtar singh,
SAIF, Punjab University, Chandigarh, India. Also, Mr. A.B. Patel from the Department of Applied
Chemistry, Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, is gratefully
acknowledged.
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